Czar,
I can thoroughly sympathize! Had it happen to me (and customers) many times. Three programs I use for this problem, PestPatrol and HijackThis to find the pests, then SpywareGuard which includes BrowserBlaster to keep these pests out of my browser.
There is a newsletter on my site (
www.customcomputerhaven.com/newsletter.html) concerning this topic with download links to each of the above programs. HijackThis and SpywareBlaster are free, PestPatrol has a trial version and is not at all expensive considering the trouble it can resolve.
Since installing SpywareGuard on all of my systems, I haven't had one hijacking! I would highly reccomend this software to be installed on all computers connecting to the internet.