Mine never worked when I had our old computer--we had Windows ME, and the most recent IE. I disabled all of my possible popup blockers and thought I was all set, but all it ever would do was open the first one on the list. We got a new computer (our old one finally died), and it has Windows Vista, and SweepsPop works great, even with all of our virus and other protections.
Maybe it has something to do with Windows ME?
Anyway--just adding my two cents. I love sweepspop and it has saved me SO much time entering!