I use a program that my company uses called VET. You can find it at
www.vet.com.au
I find it is very reliable and efficent, as it picks up viruses gained through internet surfing and deletes them as soon as they try to install them onto your pc.
If it can't delete them, it shows you where to go in your files and delete them.
I use another product from them called pestcontrol which hunts down all those nasty registry keys which install on your computer from net surfing and doggy software.
How ever pestcontrol has a bit more work to catch alot of the older popups and webscreen hijakers.
Regards
Lord Vader