work group should not matter...

between your PC's try mapping drives directly rather than browsing. For example: PCa and PCb - on PCa map a drive to \\PCb\"shared folder name"\ another way is to use the direct IP address of the machine with the shared folder. For example: \\192.168.1.10\"shared folder name"\ (trailing backslash not always required). If you don't have it on already you need file and print sharing enabled on your PC's. Another thought is if your using any of the default shares sometimes they end with a $ symbol...this hides the share from general browsing but you can still map to it example: \\PCb\c$

These are just initial thoughts on basic home networking. Some versions of XP and vista may have funky security settings that you have disable or "allow" before actual sharing will take place. You definitely do need to make a share though, it doesn't just magically happen for example if you wanted share the entire hard drive of one computer the easiest way is to right click on the C drive and choose Sharing (or properties and then go to the sharing tab). From there you can set a share, number of allowed users etc.