I have a virus and need help to remove it?

I was infected by a phoney video codec, and my desktop now has a red biohazard symbol and a message that says "YOUR PRIVACY IS IN DANGER DOWNLOAD PRIVACY PROTECTION SOFTWARE NOW"

I am not stupid, and I know a little about computers, so I do know that this is a virus it is trying to trick me into downloading software that will infect my computer further. Everytime I remove the wallpaper (its a web page wallpaper that is clickable, and I have to manually remove it), it always comes back in a couple hours. To make matters worse, my antivirus, McAffee, is disabled and I cant fix it. I think that the virus may be messing with my antivirus too. Please help, I am desperate. I even uninstalled Internet Explorer because thats where all the pop ups came through and it has a phoney toolbar called the "bonsws."I am using firefox. The popups are still coming. Without antivirus I am completely out to other viruses. Please give me simple directions to remove this virus.

I have a virus and need help to remove it?free antivirus download

I had a similar problem a year or so ago and thought that I would have to reformat and start all over.

I talked to a computer guy where I work, though and he said no need to do that. He fixed it for me without having to reinstall windows. It took him several days, though, so it is not an easy job, but can be done.