If you have viruses then your first priority should be getting rid of them. Install Avast or Nod32 antiviirus with latest updates.... And run a full system scan. Then scan with ad-aware or spybot.
Formatting your disk is the last option...
Do you want to reinstall Vista?
If yes then you can boot your comp right from your Vista Disk. It has an inbuilt partition manager. Use it instead of other boot disks.
Free alternatives To Ghost:
HD Clone 3.7
Or Choose from these , Hope its an easy choice