Yesterday, I have installed Vista and my Internet stopped working. You could find that post here.

The problem is not with Vista but with the Security Software I am using, Live OneCare from MS.

Apparently there is a problem with OneCare firewall that prevents Internet connection

The solution I found out was

“The only solution I have found so far is to turn off the OneCare firewall (until they release a fix) and to turn on the regular Windows Firewall.  It warns you against this and my OneCare is now red, but I can connect to the Internet through my wireless router.”

from a forum post.

-Cheers