The XP machine should still be able to see/access the shares I think.

Do you haev a firewall up on one of the machines?

Try adding a second account and then making sure that you give both permission, and access to the file for that user.

I'm running a Win 2k3 Enterprise as a PDC and I have a couple computers not ont he domain that can access some shares just as long as they supply the right password and username.