That sucks man I feel your pain. Not too long ago I had to re-install WinXP 3 times in one month due to stuff auto-installing and taking over my machine.
The last time I re-installed Windows I did the following, and haven't had any problems since:
- Stop using Internet Explorer and use Firefox or a more secure browser
- Use an antivirus program like Norton AV 2005
- Install Ad-Aware and run it daily
- Install Spybot S&D to monitor your systems
- Make sure you have all the latest Windows updates
Actually, since I stopped using IE I haven't had Ad-Aware find anything, whereas it used to find tons of stuff daily. Hope this helps.