i had the same problem with IE7 even with a pop up blocker on as u get with the new ie7. i know you will say thats worse than firefox but hear me out you have 2 very simple solutions download a new browser like maxthon which is great by the way which has a working anti popup or get adaware se plus which runs in live protection mode which also has a nifty little ad blocker scanning for adware alone will not work but u need something that runs live.
i reccomend adaware SE PLUS by the way check out that maxthon its worth a look