"Reinstall from scratch" is what I originally said: force boot from CD, format drive, install OS. If done properly there is no chance for something to hide.

Anyhow, I agree with the following: "the only way to know for sure that you got it is to wipe the hard drive and start over."

If you want to be unsure you got everything then that's your call. My experience is that if one is unsure then one is probably wrong. But it's your computer so obviously you should do as you please and regard my comments as nothing more than unsolicited advice.