free space wiper

Hey Kimo- I've used Eraser before and it seemed to work fine:

http://www.tolvanen.com/eraser/download

I have been looking around the net. I would like any suggestions as to what program to use to wipe the free space on my hard drive. Using windows xp. I do not mean a total wipe of the hard drive just the free space so that deleted files are actually deleted.