Slow network with network neighborhood

I am running a 2003 server with mixed win2000/xp clients.
All seems fine except that the network drive becomes
increasingly slow the further down the directory structure
I go. If I map a drive letter it works as expected. This
only seems to affect the XP machines. Does anyone know of a
reason for this or a method of correcting it?
The network I am running has a 1GB server connection and 25
100MB connections. There are rarely more than 6 or 7 users
on at any given time and network load is low.