Spybot is good, but you'll need more than one spyware scanner. In some cases, one will detect something that the other doesnt. If you do eventually end up reinstalling, what I recommend is to get your system up to the point where you have all your apps installed and configured, then use something like Ghost to image your disk.
What I've found, is that no matter how much scanning and maintenance I do with my system, it'll eventually start bogging down over time, and the only thing to get it performing the way it should, is to nuke the system and start again...