Slow network Logon

We have XP pro machines in our lab that logon to
a W2K Server very slowly…1-3 minutes after password is entered. And in the same lab we also
have Win 98 machines which are much older that
logon to the same server very quickly. What could be the problem…this is happening in 5 different schools and with 5 different servers
Why is XP so slow? We have almost no network traffic.