Quote of the Day - The only one who can tell you "you can't" is you. And you don't have to listen.
Microsoft has [finally] released a beta version of an anti-spyware program. McAfee (costs) and Ad-aware (free) are other alternatives.
You can download it here (free).
Beta software is generally untested, so it's probably better to go with a pre-proven solution, at least for now. Maybe after six months it will something to think about. But if you've got a ton of pop-ups, something is better than nothing.