Slow Lan access XPPro to XPPro

[Bob Clements]

I have a lan with 2 XPPro PC's, and 2 W98PC's. The 98
machines access the XP machines no problem, but the XP
machines communicate very slowly with each other. e.g. a
13000 line Excel spreadsheet resident on one of the XP
machines will load across the network to a 98 machine in
15 seconds but load time from the XP machine to the other
XP machine takes 2 mins 30 secs. All machines have fixed
IP addresses, latest service packs. Have tried disabling
virus scanner and other suspects to no avail.