I have an annoying virus

I have a problem, and I think it originated with one of the shitty fwdfwdfwd emails my mom sends me.  My computer gets a popup every so often saying that Windows Firewall has detected Win32.Zafi.B virus and has a link going to an antivirus program you can buy or trial download to wipe it. I have AVG antivirus on my computer and I used some of the online antivirus tests, and the just found a trojan or two and is still here after the other stuff was treated, Anyone know what it is or how to stop it?

delete system32