I'm also looking for a portable app that would allow me to overwrite unused sectors of my HDD at work, and/or erase files completely by overwriting the space they occupy in the HDD several times (preferrably customizable, i.e. once, 3x, 5x, or more) using random chars.
I'm, essentially, looking for a portable version of Eraser (http://sourceforge.net/project/showfiles.php?group_id=37015) ... one that doesn't muck with the registry. I don't need the scheduler feature.