Here's what you'll need to do:
First of all, its like 100x easier to access the Mac from the PC than visa versa. So do it that way and your life will be a whole lot easier...
On the Mac:
1. Click on the Apple Menu (top left) and then click on System Preferences
2. Navigate to the Sharing System Pref
3. Check the box that says Windows File Sharing. It may prompt to enable your account with windows file sharing. Make sure you do that. If needed, authenticate. Now your Mac is all setup to share files. Yup, thats it on the Mac side...just check 1 box!
4. Go back to system preferences and then click on Network.
5. If you're using Ethernet (wired), then double click on Built-in Ethernet, if using AirPort (wireless), then double click on AirPort.
6. Under the TCP/IP tab (should be there by default), write down the IP address. Its probably either a 192.x.x.x address or 10.x.x.x address. If you get a 169.x.x.x address it may or may not work as you could be running into network issues.
Close out system preferences and then go to the PC
On the PC:
1. Right Click on My Computer and then click on Map Network Drive.
2. Type in \\ipaddressofyourmac\yourhomefoldername and press ok, enter, or connect or whatever it says there...
So it should look something like this:
\\192.168.1.1\michael
If you've typed everything in correctly, it should prompt for a username and password. The username is probably already filled in. Make sure its the username of the Mac, NOT the PC! Then if necessary, type in the password of your Mac, NOT the PC! It should then map your home folder of the Mac on your PC. Now you should be able to transfer files back and forth from the PC to the Mac and visa versa. If you can connect to the Mac from the PC then its not really necessary to try and connect to other way (Mac to PC) because you can take files from your PC to the Mac and Mac to the PC by just mapping the drive on the PC. And sense Macs can't write to NTFS, its probably a better way to go anyways (PC to Mac).
Also make a note that software based firewalls may try and make it difficult for things like this to work. One reason why I absolutely HATE software based firewalls. So I would make sure that the Windows XP firewall is disabled. Keep in mind that sometimes a windows update can kick the firewall back on without you noticing. Other firewalls such as ZoneAlarm, or Norton Internet Security may also effect connecting to network computers depending how strict your settings are. If you have a router, then you don't need a software based firewall because the router is doing the work before it gets to your computer anyways (well at least incoming traffic). Hardware based firewalls are MUCH easier to configure and IMO, more reliable.