You only need to prevent recovery of your own files if your selling or giving away your computer (or throwing it in the trash). But in this case, a much better option would be to reformat the entire hard drive (including writing the zeros) and reinstalling a fresh OS. It usually only takes 10 minutes or so that way, because the system doesn't have to carefully tip-toe around files you want to keep (files are usually written in many random places on the disk), but rather writes a straight line of zeros. I did a 90gb hard drive recently this way, and it took like 10 or 15 minutes.
Why do you want to prevent yourself from seeing your own files?
SIDENOTE: My 1,111th post!