Desktops: Network Slows XP?

Slow Motion

Without knowing exactly how your network administrators have your intranet set up there's alot that could be going on.

Could be one or a combination of the following affecting your speeds:

Number of active users on the intranet all pulling information at once;
types of intranet applications running processes;
peak periods of access;
your domain controller being flooded/over worked;
your distance to the domain controller;
network traffic restrictions such as QoS quota;
IT department running various scans to include network bottleneck monitoring;

I'd track the issue for a week straight and then forward your findings to you local IT department and see if they can clear it up, it may be something they aren't even aware of.