I am running Windows Vista Ultimate. I went to the add/remove Windows components tool and unchecked "Internet Information Services." However, when I access http://localhost/ the IIS 7 default page is still shown. I would expect no response.
Looking at your comment to LuckyLindy's answer, it seems you already tried removing it from Vista's add/remove programs, AND you disabled the service, yet you're still getting a response from localhost.
Assuming it's not a browser caching thing, you may want to use a tool like TcpView to determine which process is listening on port 80. It could be something other than IIS 7 that's listening and responding.