Omg I'm really scared just got virus on computer?

i don't know how I got the virus but something on my comp popped up and said it was an email worm or something!!! I'm running a virus scan rift now using avg free edition but there's this other program called Internet security 2010 that came up and I don't even know what it is but it keeps telling me to sign up but I can't cause it costs money. the virus also changed my wallpaper and it says that my computer has been infected. I'm so scared haha what do I dooo????