@W3bbo: A simple google toolbar infection combined with some entries in the Hosts file could exhibit the behavior as well. It may not be a rootkit. Then again, if it is a rootkit you need to blow that partition away and recreate it. If you don't take the approach to just reinstall Windows, then you will spend more time analyzing and trying to clean and then more time still wondering and watching if it was actually clean.
Even if the infection is not a rootkit, what is to say that the infection has not put in enough hooks to always have a backdoor in place no matter how many different virus cleaners you run on it. Whack-a-mole style.
Save your data files and blow that partition away.
I presume you have other machines with which you can download the Win7 ISO and use the Windows 7 USB/DVD Download Tool ( http://wudt.codeplex.com/ ) to reinstall.
There is also the option to do an in place upgrade of Windows 7 to see if that might work. Although I don't know how it would distinguish a viral hook from any other legitimate hook.