firefox is worth using... I suggest though once you do get it fixed DL AdAware SE and Spybot: Search and Destroy from www.download.com

Both work really well together, Spybot gets the nast virus stuff while adaware does better at tracking cookies. If running these two programs now doesn't fix the problem either then reformatting the hard drive is the last option. Just make sure you have the windows discs. (not vista....ewww.)