Grumpytoo,
There are many programs that will search your computer for spyware and related annoying software. Possibly the best is called "Ad-Aware". It is a free download, and can be obtained from:
http://www.lavasoftusa.com/support/download/
After downloading and installing this program, allow it to run. It will search your computer and see what software is installed that might be causing the random popups.
Another good idea is to obtain a virus scanning program. One such program is made by Panda software: http://www.pandasoftware.com/activescan/com/activescan_principal.htm This program can be run online from within your browser.
As a final note, take care when installing seemingly benign software. Especially beware of anything that says it will "helpfully" install GATOR or GAIM software. That is one of the worst offenders of spyware and popup software known.
I hope this helps,
Paul Lalli