This is another trick that power users apparently are well adjusted to but haven't publicized.  It's not limited to Vista or IE7.  Just type the domain name you want in the address bar and then hit ctrl-enter to prepend "http://www." and append ".com".  Once again lifehack, you have made me a more effective human.

http://www.lifehack.org/articles/technology/quick-com-address-bar-shortcut.html