It is highly unlikely nowadays that you would get a virus which makes you resort to the above but you can use system restore or just use the factory reset disk. You should make regular backups of your documents, music, favourites etc. though. If you reinstall windows you will eliminate all viruses but as I said before it is highly unlikely that you will get such a virus if you keep your AV up to date and use something like Spyware Terminator. You could also use Acronis which will do an exact copy of your HD and you can then copy it back to the HD.