Back when I used to fix computers I never sucessfully removed a virus with an anti-virus tool since Windows 95 was released. They're all rubbish, without exception.
I'll give you a hint about the anti-virus community: On the Macintosh there where no virus' for a good number of years, there's now a handful all of which where quashed by Apple patching the vulnerability out of their OS. However before the first OSX virus there was over 10 anti-virus tools for OSX, many disappeared when the first virus was descovered.
The anti-virus industry is full of crooks.
What's more the protection software that's available is universally inadequate, corporate programming practices just cannot compete with the college kids who make this stuff.
Big virus databases wont help either, a virus is mostly only a threat to normal users when it is "in the wild", ie: Just after release. It takes ages for the anti-virus companies to respond to real security threats, so the only real protection you have from a virus your software is giving you no protection against.
The virus writers know the tools out on the market, dont be fooled into thinking that this heuristic guessing things will protect you, they wont. The anti-virus software exists before the virus is writen, ergo, the virus is going to ruin your day anyway.
So accepting that anti-virus software will neither remove a known virus, and your most at threat from unknown virus, what can you do?
Well personally I recommend using newsgroups for porn rather than your web browser, and don't use bit torrent.
Prevention is better than cure, just dont be fooled into thinking having 2 or more anti-virus programs is going to do you a scrap of good - it will do good, but only for a fat cats carribean cruise.
Once infected, either get it professionally cleaned, delete windows folder and reinstall, or educate yourself in methods of removal.