Some folks are having issues with the new McAfee retail program on Vista.. Try disabling it to see if it fixes the problem..
Is the connection wireless or wired?
It's also important to make sure the ethernet and wireless adapter drivers are up to date. Likewise with your modem or router's firmware. Update it if possible.
Links to other discussions about that issue:
Hope this helps.
I am using a T-com 1054 Modem and when I go on the Internet using my username and password from the computer I log in fine. But when I put the Username and password in the modem,The modem goes online but I can't access the internet from the computer. When I use a second computer with windows XP it works fine But not with Windows Vista. Is there a special setup I need to do? If its in the forum already can you please tell me where. Thanks germansal