Key thing that antivirus suites can't often deal with (short of suggesting you restart in safe mode then rescan), is with areas that can be termed 'hives' for virii.. the most common of these is system restore points, since they are unchangeable files that the system protects from modification. Now, assuming the virus has got past that, it is then safely nested on your machine... a lot behave this way, so the best advice is to disable system restore in the system part of control panel.
I recommend Kaspersky for killing active virii, and even as a shield, though I usually run it disabled, only scanning when I periodically feel the need/have the time. It is good because it allows you to set up rules for the behaviour of applications, preventing them from doing certain things by blocking them when they attempt.. or trusting them if that is what you choose when it pops a warning. At first the warnings are annoying, but over time, it learns and results in quite a secure system indeed... but like I said, I disable a lot of that crap.