Problem with Win XP

Hi all, I have this problem, and to be honest I cannot figure out how to fix it. Recently, people start complain about the login screen hang on there forever. They just have a message that say, “loading the profile…. ” in some computers, others just have a blue screen.
Has any one have this kind of problems with Win XP. Because I have other Lab with 25 pc’s on Win2k and the same users can login with no problem. Only when they go to the Win XP machine they have this problems.

I run Win2k Server, XP and Win2k Workstations.

Any help will be apreciated. Thanks!!