Sometime Spyware and Adware can sort of protect and reinstall itself. It can take several different programs to remove it all. I am currrently using 4 pieces of software to keep my system clean:
Microsoft Antispyware (downloadable from microsoft.com and also has active security agent that monitors real-time and stops various nasties installing themselves).
Ad-Aware from Lavasoft.
Spybot Search & Destroy.
The Yahoo! taskbar - has Anti-Spy program.
Try running the others before you run Spybot again see what happens.
Good Luck!
RBG