MS Office Docs take 20-30 seconds to open

Since upgrading to Windows XP users have experienced 20-30 second delays
when opening & saving Word or Excel documents. This is an intermittent
problem. Sometimes the Word, File Open window says Open (not responding).
Sometimes when navigating folders/directories within the File, Open window
in Word or Excel it takes an age for the folders/directories to display.
The issue sometimes happens when users have been away from their pc's for
a while, the first doc they select takes 20-30 seconds to open.

We're running NetWare 6 Support Pack 5 on our main server and branch
office on two other servers that suffer the same problem. The client
version is 4.91.

Are there changes I can make to the client settings to overcome this issue?