Fox, as with all virus scenarios, boot up in safe mode and run your antivirus. If that doesn't cure it, you're pretty much fucked. Reformat time. >_<
Next time, don't double-click on a flash drive's icon. Use right-click and select "explore". It also helps to disable Autorun.
Next time, don't double-click on a flash drive's icon. Use right-click and select "explore". It also helps to disable Autorun.