Authentication problems

I have a user that can log in and it appears that he hits
the domain controller. But when he try's to open a mapped
network drive he recieves a security violation. When I
look at the security log it shows that his computer is
trying to login every couple of min and of course locks
his account out. I unlock it and he can get in then after
an hour or 2 he is locked back out with out logging off
or any thing. If any one has any ideas I would appreciate
it.

Basic set up is Windows XP all users, 2000 small business
server. in an active domain. Any questions let me know I
have had this problem for 3 months now. (only trouble
shoot it when it is a priority once a week)

My email is
Remove the dog for legitimate e-mail.