I will second, triple and quadruple the recommendations by others to start using Firefox and STOP USING INTERNET EXPLORER. It is the worse piece of crap browser out there. I seriously believe Microsoft leaves their browser the way it is because they get payoffs by spamming companies to leave it that way.
Firefox is a superior browser in everyway when it comes to security and stopping spam. With Firefox I use Lavasoft Ad-Aware and Spybot. I think these are all you need. I almost never get spam or popups of any kind. I also have the Norton Suite which has extra protection against popups and can even disable flash ads.
If you are cleaning your system out, I recommend Ad-Aware and Spybot and start using Firefox immediately. Also download Webroot SpySweeper. It is an excellent spyware program better than the others I listed, but it has a subscription fee. However, it has a 15 day full access trial. Use it a couple times during its trial to get your computer clean and you may not ever need it again.
Conveinent links:
Firefox
Lavasoft Ad-Aware
Spybot
Webroot Spysweeper 
