If you are looking for some free software then I'd like to recommend Avira antivirus, Advanced System Optimizer, TuneUp Utilities 2009 and CCleaner. With this combo I'm sure that you'll be 99% free of viruses or any nullwares. Those are the ones I use BTW
i have on my computer Kaspersky and NOD32 and i'm very pleased with both of them i haven't had a virus for a very long time