You can do that among other things with this app:
http://www.heidi.ie/eraser/
Install it , rightclick on the drive/partition in "my computer" and select "erase free space". Then all free space (and thus all deleted files) get erased. You can't specify an single file after it has been deleted, but you can erase single file before you delete them (well , you dont have to delete them after erasing them ofcourse , lol)