Is anything else slower on the xp machine? Like accesing other web pages or stuff?
How much memory does the xp machine have?
XP have firewall on?
One thing you could try is to turn off some of the unneeded "services" that are running on the xp machine. go to
www.blackviper.com and check out his "xp services configurations"....I usually use the "safe" one with a few small exceptions....but if you check that out you see that XP has a lot of "bloat" running that you dont need....junk like "smart card helper, portable media serial number, alerter, messenger" etc etc.
JP