Assuming, of course, that you've already run LavaSoftUSA's "Ad Aware", that you've already run MSCONFIG.EXE and cleaned any extra crap out of the startup group, the run lines in the registry, etc., and that you've already done a complete virus scan. At that point, it becomes just one of those things where you just need to reinstall Windows once in a while. In that case, the Corporal Hicks method is the only answer.

"Corporal hicks?! But he's just a grunt!

Uh, no offense..."

"None taken."