Hi,
XP home uses a simplified SMB sharing protocol. Once you set a folder for sharing, every pc on the network can access that folder. In XP professional, I believe this is called easy sharing.
The normal SMB sharing does a check on username and password. You can give specific rights to every user. (For instance read only.)
So, you might try to find the differences between the 2 to pinpoint to your problem. Maybe you have to leave the User field blank or something.
regards.