Adaware, and Spybot. If you need more then that you'd save time just writing the important data to a CD/DVD/NAS, and formatting with a fresh install.
I prefer AVG to Avast (free) and Nod 32 to them all ( not free ).
If your using IE and spyware has screwed your browser you might be able to save it with Hijackthis but its mostly a lost cause.
Run Adaware, and Spybot in safe mode if it can't be removed in normal XP mode.
Always update your OS, Anti-Spyware, and your Anti-Virus. Run a scan monthly like you change your oil every 3000 (5000-6000 whatever interval you use) miles and your golden.
Clean out the registry every 6 months with something like CC Cleaner and it should run newish.