Remember that most will not remember or know how to install these OSes.
http://www.google.com/search?&q=hard+disk+zero+fill finds the Zero Fill method.
All gone except for CIA/FBI retrieval methods.
What is the best way to sanitize a hard dirve? I have several old computers and I want to make sure all data is gone and not recoverable. All are Windows based 95-thru XP.