Unknown user when connecting through XP

I have set up a small workgroup, one XP prof and the other being Win NT server (Also changed to 2000 server).
I have assigned IP addresses and both stations can ping each other and can ping the name of the pc as well. Both ip’s are correctly id’ed when using NSLOOKUP. The XP client is able to browse to the NT/2000 station but the NT/2000 station cannot browse to the XP station.

When you try to browse to the XP station you are aske for a user ID and password but evan using the administrator account you are told that username and password are incorrect. Any suggestions?