Can't access Microsoft Update through ICS

I have my laptop networked through a wired router to my desktop machine, and
the laptop shares the internet connection established by the desktop. With
the laptop I can browse the net, receive virus signature updates, etc, but
when I try to log on to (the web page) for Microsoft Update, it just hangs
and never opens the web page.

I've tried disabling the firewall and anti-virus on both machines and still
no-go. If I just let the laptop connect to the internet through its own
modem, then it will work.

Any ideas what might be wrong here? (WindowsXP Home Edition, SP2 on both
machines).

--
Gregg C.