I asked that same question some time ago and Greg gave me the following useful info. I used it and the problem was almost totally eliminated.

Jeff,

Go to:

http://www.lavasoft.nu/index.html

and download Ad Aware. It will rid your computer of the software that you intalled either accidentally or on purpose that is letting these pop-ups in.

Just be aware that there is NO pop-up advertising done on this site.

Greg