That’s because you are infected, You have to remove the crap that’s allowing the pop-ups to happen.
Run a virus scan
Run Spybot Search and Destroy.
Clean your system.
Tip for ya, avoid installing 3rd party crap that comes in software installations. Example: Toolbars.
I don’t know if you like FireFox or not, but I would install that which comes with a pop blocker. Then for a add-on program use No Script which is software that allows you to control scripts that run on the page. Once you have figured out how to use No Script in conjunction with FireFox you should never see another pop-up.
If you don’t want to use FireFox then clean the junk off you system, then use a pop-up blocker with IE.