you won't find a better set of free tools than this
http://free.antivirus.com/clean-up-tools/
I highly recommend HijackThis for finding spyware, however, be very careful as it doesn't distinguish between what is supposed to be there and what isn't. It just finds stuff for you. From there you can either fix or break your PC 
Also, it isn't Vista Compatible, but it is the one I've used in the past and very good.
From the list You could try HouseCall or RUBotted, which I've never used, but it's free.
Also, CWShredder works great if you know you have CoolWebSearch installed which is by far the most annoying spyware to remove. I'm not sure if CWS infects Vista machines, and CWShredder isn't listed as Vista compatible.
EDIT: malwarebytes is good too. You can ask on their forums - http://forums.malwarebytes.org/ - and they'll help you out and make sure you solve the problem. you'll get better support there than pretty much anywhere else that I know of.
As a side note, I'm so glad I don't know any more stupid teens who get their PC's infected all the time and insist on me fixing it for them
