I highly endorse ad-aware to remove spyware and other unwanted leaches.
For elliminating unwanted pop-up windows all together, I highly endorse EMS Free Surfer MKII:
http://www.webattack.com/download/dlfreesurfer.shtml
Both of these softwares have received 100% positive reviews.
If you use kazaa, there are several tricks to remove the spyware but maintain functionality. Check out the following for how to do so:
http://www.geocities.com/little_kingston77/