I don't know where you heard that but I don't believe it's possible for people to pull your personal info after you've just formatted your hard drive. Formatting wipes out absolutely everything including the OS (Operating System such as Vista or XP). Believe me if that were possible then formatting would serve no purpose, viruses would keep coming back, all the issues you had before you formatted would still be there, etc. Plus people wouldn't complain about losing all their data if this were possible, as they could just get all their games and files back. So in my opinion that is not possible. But anyways.
As for formatting your hard drive, you will have to re-install the OS no matter what, it's just how it is. It doesn't take that long, half hour tops as long as your computer is decent. I'm assuming you don't have your OS cd which is why you don't want to have to re-install the OS. Well you could visit your computer manufacturer's site. A lot of times they have the OS cd's up for download and you just burn it to a cd and you're good to go. Like I said if you truly want to wipe everything off your hard drive then re-installing the OS is inevitable unfortunately.