The mac will not share all of its folders. It The mac's workgroup can be changed by going into the Utilities folder as an admin and using the app called 'Directory Access'. Change the SMB CIFS attribute to your pc's workgroup name.
That should cover everything!
I'd been battling for 24 hours to make my MacBook connect to PC - that little gem above was what finally allowed me to do it.
Many thanks.
For anyone else trying to do this who was a clueless as me these steps might help (I was using XP, OSX Tiger, and a cross-over cable although I hear a standard ethernet cable will work fine on MB and MBPs) :
1 Findout what your PC workgroup is (right-click "my computer"
-> "properties" -> "computer name" tab will reveal the workgroup name. If one is not specified you need to "set up a small home or office network" in "My network places" - during this you will be able to make a workgroup name (keep it simple)
2 Findout your PC IP adress - "Start" -> "All Programs" -> "accessories" -> "command prompt" -> in the command prompt type "ipconfig" - your IP address is one of the first things that will be listed.
3 In XP - now go to "show all my connections" - right click that LAN (ethernet) connection that your bastard computers are connected through. Select "properties" - select "Internet Protocol...." in the box then click "properties." In the new window select "use the following IP address." Enter the IP address you got in step 2. Subnet mask will automotacilly fill in - if not 255.255.255.0 should do the trick. Apply the changes.
4 You may want to consider taking down your firewall at this stage and making sure you have a shared folder.
5 On OSX Tiger - Do the usual steps of turning on windows sharing/personal fiole sharing and making sure that an account is selscted to do this (see above... and google) - you'll get your mac IP address this way as well.
5 Do what it says in the quote at top of this post using the workgroup name you created/found earlier.
6 Still on Mac - Finder -> "Go" -> "Connect to server" -> in the "server address" box that appears type "smb://
your pc IP. You'll be asked for a password - your mac password will do it. Start sharing! Go to yor XP and click "view workgroup computers" in "my network computers" -> your mac should appear.
If the above doesn't work try the other various methods that the net has to offer and eventually something will happen.