I had already deleted all my files and emptied my recycle bin before i learned of eraser. How do i overwrite the files now without having to totally erase the entire hard drive (operating system files are packed up for a move)?
You can't do this with eraser. There is an old program called Restoration available here: http://www.snapfiles.com/get/restoration.html that will do it.
Just click on search deleted files and when it finishes finding all your files select 'delete completely' from the 'others' tab.