HELP! Computer help desperately needed!

Well, in the time between asking for anti-virus and anti-spyware suggestions and actually updating, I got hit with a nasty one. (Again, I am thanking fate for the laptop, as I can communicate via it until I get the desktop fixed!)

( What happened and what showed up )

Question is - how do I disinfect the original hard drive? Can I do so with loading an anti-virus program now (presumably out of the box, as I dare not type anything important on it right now), or do I have to wipe all and start over? And either way, the luddite types plaintively - HOW?