format c: My favorite dos command
My preference when doing this is get Windows, an antivirus and a firewall loaded onto the machine before allowing any access to the internet. Hit the register later buttons during the installs, have the cable unplugged, etc. Then connect to the internet and get all the windows patches, antivirus and firewall updates applied. I'm not a fan of spybot, adaware or hjt. Personally I think they are more bother than they are worth. A good antivirus and an effective firewall can provide adequate protection. Don't forget to scan your backups to see if you have saved any interesting viruses.
Regards
Stoney