Sounds like the permissions for the drive haven't been shared with the rest of the folders. I have seen this before in XP Home. Just open Windows Explorer, and right click on the shared drive. Open the Security tab, and click on Advanced tab at the bottom. Select Everyone in the list that pops up (Permissions tab). Now check the box at the bottom that says "Replace permission entries on all child objects..."
Wait until it finishes changing permissions (could take a bit), then try accessing the share again. Should work now.
I think.
Cheers
Mick