Norton has a free online virus scanner that's reliable.
Go to :
http://www.symantec.com
....then click the SECURITY RESPONSE link in the menu bar across the near-top of the screen. When you get to the Security Response page, look in the list of links called VIRUS DEFINITIONS, and click the link marked
"Free Online Virus and Security Check"...That utility will install a temporary scanner and virus definitions on your machine to give your mem and drives a clean sweep for virus's.
P.S....next time you reformat your drive (and if you didn't do this already...), be sure to use a disk wiping program that clears the whole master boot record as well as the data tracks...I've read articles of persistant virus's that hide in the MBR during reformats....Some of those articles were at Microsoft itself. Just search under "virus master boot record"
...also, make sure any extra slave drives are unplugged during the OS reinstall, until you get a good antivirus program installed, just in case a virus is hiding on another drive, waiting to infect your C drive as soon as you get windows reinstalled. Hook it up later, once your system is updated and secure.