XP vs other OS's

Task: Open Windows Explorer, browse to a Win2k or Win2k3
server location, and click on a folder to view its
contents. Wait time for contents to appear in right pane
of Explorer: XP - 20-25 seconds; other OS's - none. Also
no wait time foor XP if server location is NT4. What
gives? And don't tell me I'm crazy; I've been trolling
the newsgroups for answers to this question, and there are
many of us out there with this problem, but so far no one
has the answer.