To erase files and securely wipe free space in windows I would suggest using :
eraser -
http://www.heidi.ie/eraser
To securely wipe the entire contents of your hdd I would go for:
Dban -
http://dban.sourceforge.net/
Both are free and do a decent job. Eraser gives you the option of various wiping levels wile dban only does the 35pass Gutmann method[0] (accept no substitutes
[0]
http://www.cs.auckland.ac.nz/~pgut00...ecure_del.html