OK, this question comes up all the time, "How do I share files between my Mac and PC". So, here is the answer. I'm hoping we can make this "Sticky" and save everyone time 
I think I have remembered everything, if you think there is somthing I've missed then please post and let me know.
Networking Windows (2000/XP/2003*) with Mac OS X (10.3/10.4)
Information you will need to know
• The IP Address of your PC (Start > Run > CMD {return} > “ipconfig” {return})
• The IP Address of your Mac (Applications > Utilities > Terminal {Run app} > for ethernet connection “ipconfig getifaddr en0” {return} or for wireless "ipconfig getifaddr en1" {return})
• The workgroup the PC is in (Right click on My Computer, select Properties, and select the Computer Name tab)
System Configuration
It is important that the account you log in with on your XP system has a password set, if it does not you will not be able to login to your Windows share from OS X.
You need to put your Mac in the same workgroup as your Windows PC. To do this open “Directory Access” (Applications > Utilities > Directory Access). Click on the padlock in the bottom left corner to make changes; you will be prompted for your password. If “SMB” is not ticked off, then tick it off. Select “SMB” and hit the “Configure…” button. Now enter the name of your Windows workgroup. In my case the name is “AD”.
http://upc.*************/uploads/forums/mac_directory_access.png
Setting up the PC to share files
You need to create and share a folder on your PC that you will then access from your Mac.
To do this create a folder (or select and existing one) right click on it from Windows Explorer and select “Properties”. Select the “Sharing” tab and share out the folder. I’d recommend you use a one word name for the share. For example “mac”, not “Apple Mac Share”, it just narrows the risk of complications.
http://upc.*************/uploads/forums/Windows_shared_folder.jpg
Setting up the Mac to share files
Open “System Preferences” (Applications > System Preferences). Go to “Sharing” under “Internet & Network”, and tick off “Windows Sharing”, and if it doesn’t start by itself, click “Start”. This will share out your entire home folder.
http://upc.*************/uploads/forums/mac_sharing.png
If You're running Tiger (10.4), you will also need to click the "Accounts" button and tick off the box next to your account name so that OS X knows to share out your particular home folder.
http://upc.*************/uploads/forums/mac_enable_acc_share.jpg
Accessing your Mac from your PC
Click “Start > Run” and enter “\\192.168.1.2\edesignuk”, replacing the IP address with the IP address of your Mac, and “edesignuk” with the short user name of your account in OS X. When asked to authenticate enter your Mac accounts short user name and password. All being well you should now be able to see you entire home folder on your OS X system. You can also map this share like you would any other Windows network share so that it is accessible from a drive letter.
Accessing your PC from your Mac
To mount a Windows share on your Mac, click on your desktop so that Finder is the active application, from the Finder menu go to “Go > Connect to Server”. In the “Server Address” field enter “smb://192.168.1.3/mac”, replacing the IP address with the IP address of your PC, and “mac” with the name of the Windows share you created earlier.
http://upc.*************/uploads/forums/mac_connect_to_server.png
When asked to authenticate enter the name of your PC in “Workgroup/Domain” (Unless your PC is part of a domain and your PC account is held on a domain controller, in which case enter the domain that you normally log on to Windows with). For “Username” and “Password” enter the username and password which you use to log on to your Windows machine with. Click ok and your shared folder should be mounted as a network drive on your desktop.
Get error "The alias "<shared folder>" could not be opened, because the original item cannot be found."?
Read this post by EWTHeckman.
http://upc.*************/uploads/forums/mac_connect_to_pc.png
*Windows Server 2003 Authentication
By deafult Windows Server 2003 will try to encrypt everything sent to and from it. With this enabled you will not be able to log in to the share from your Mac.
To fix this there are a couple of options.
Case 1, your server is nothing more than a regular file server. In this case open up regedit (Start > Run > "regedit" {return}), and navigate to HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Services \ LanManServer \ Parameter \ RequireSecuritySignature, and set it's value to "0".
Case 2, your server is also a Domain Controller. In which case you need to open the DC's Security Policy (Administrative Tools > Domain Controller Security Policy). Navigate to Local Policies > Secuiry Options, and disable "Microsoft network server: Digitally sign communications (always)" & "Microsoft network server: Digitally sign communications (if client agrees)". Reboot your sever, and you should be good to go.
I think I have remembered everything, if you think there is somthing I've missed then please post and let me know.
Networking Windows (2000/XP/2003*) with Mac OS X (10.3/10.4)
Information you will need to know
• The IP Address of your PC (Start > Run > CMD {return} > “ipconfig” {return})
• The IP Address of your Mac (Applications > Utilities > Terminal {Run app} > for ethernet connection “ipconfig getifaddr en0” {return} or for wireless "ipconfig getifaddr en1" {return})
• The workgroup the PC is in (Right click on My Computer, select Properties, and select the Computer Name tab)
System Configuration
It is important that the account you log in with on your XP system has a password set, if it does not you will not be able to login to your Windows share from OS X.
You need to put your Mac in the same workgroup as your Windows PC. To do this open “Directory Access” (Applications > Utilities > Directory Access). Click on the padlock in the bottom left corner to make changes; you will be prompted for your password. If “SMB” is not ticked off, then tick it off. Select “SMB” and hit the “Configure…” button. Now enter the name of your Windows workgroup. In my case the name is “AD”.
http://upc.*************/uploads/forums/mac_directory_access.png
Setting up the PC to share files
You need to create and share a folder on your PC that you will then access from your Mac.
To do this create a folder (or select and existing one) right click on it from Windows Explorer and select “Properties”. Select the “Sharing” tab and share out the folder. I’d recommend you use a one word name for the share. For example “mac”, not “Apple Mac Share”, it just narrows the risk of complications.
http://upc.*************/uploads/forums/Windows_shared_folder.jpg
Setting up the Mac to share files
Open “System Preferences” (Applications > System Preferences). Go to “Sharing” under “Internet & Network”, and tick off “Windows Sharing”, and if it doesn’t start by itself, click “Start”. This will share out your entire home folder.
http://upc.*************/uploads/forums/mac_sharing.png
If You're running Tiger (10.4), you will also need to click the "Accounts" button and tick off the box next to your account name so that OS X knows to share out your particular home folder.
http://upc.*************/uploads/forums/mac_enable_acc_share.jpg
Accessing your Mac from your PC
Click “Start > Run” and enter “\\192.168.1.2\edesignuk”, replacing the IP address with the IP address of your Mac, and “edesignuk” with the short user name of your account in OS X. When asked to authenticate enter your Mac accounts short user name and password. All being well you should now be able to see you entire home folder on your OS X system. You can also map this share like you would any other Windows network share so that it is accessible from a drive letter.
Accessing your PC from your Mac
To mount a Windows share on your Mac, click on your desktop so that Finder is the active application, from the Finder menu go to “Go > Connect to Server”. In the “Server Address” field enter “smb://192.168.1.3/mac”, replacing the IP address with the IP address of your PC, and “mac” with the name of the Windows share you created earlier.
http://upc.*************/uploads/forums/mac_connect_to_server.png
When asked to authenticate enter the name of your PC in “Workgroup/Domain” (Unless your PC is part of a domain and your PC account is held on a domain controller, in which case enter the domain that you normally log on to Windows with). For “Username” and “Password” enter the username and password which you use to log on to your Windows machine with. Click ok and your shared folder should be mounted as a network drive on your desktop.
Get error "The alias "<shared folder>" could not be opened, because the original item cannot be found."?
Read this post by EWTHeckman.
http://upc.*************/uploads/forums/mac_connect_to_pc.png
*Windows Server 2003 Authentication
By deafult Windows Server 2003 will try to encrypt everything sent to and from it. With this enabled you will not be able to log in to the share from your Mac.
To fix this there are a couple of options.
Case 1, your server is nothing more than a regular file server. In this case open up regedit (Start > Run > "regedit" {return}), and navigate to HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Services \ LanManServer \ Parameter \ RequireSecuritySignature, and set it's value to "0".
Case 2, your server is also a Domain Controller. In which case you need to open the DC's Security Policy (Administrative Tools > Domain Controller Security Policy). Navigate to Local Policies > Secuiry Options, and disable "Microsoft network server: Digitally sign communications (always)" & "Microsoft network server: Digitally sign communications (if client agrees)". Reboot your sever, and you should be good to go.
