For free security stuff I use
spybot search and destroy,
lavasoft adaware, and
avg. Also good to use is
spyware blaster. For all the bad stuff people say about vista every time I run these they never find anything. And if the PC your trying to fix is too far gone to download and run these programs download, update, and burn
universal boot cd 4 windows which you can boot from a cd or usb drive and run without all that adware/spyware running in the background. Hell, you could run a decent business charging people $50-$75 each to pop in and run ubcd4win and remove all that crapware most people have.