ICS

I connect to xbox live via an ethernet cable going through my laptop. It
worked great with my Windows XP laptop, but now I am trying to do this with a
new Vista laptop and it isn't working. My laptop's internet connection is
working fine, and ICS is enabled on the wireless connection, but for some
reason the xbox keeps failing the IP address test for xbox live. All my
firewalls are off, though I don't think this matters. Can anyone help me out?
Someone suggested using the ipconfig/renew command, and I tried it but I'm
getting some kind of error when I do that. Maybe that's the problem here.