Slow login to win2k server.

I have just upgraded all the workstations at my company.
All the workstations have windows xp professional on them.
All the computers are part of a windows 2000 server
domain. The problem is that it takes 2 to 3 minutes to
login to the domain. Whereas, before I had pentium II's
and win2k professional and the logins were really quick.

The server acts as a login , file and exchange server. I
beleive the DNS setings are ok. I have even disabled the '
Web Client' service.

The only thing I haven't dones is updated the windows.
Could that be the issue. Please let me know ASAP. It's
really causing frustration for the employees.

Thank You

Shahzeb Hassan
Network Administrator.