Securely Erasing Files Before Selling

[Wammer]

I plan to sell my Archos 705 and want to be sure that any personal information is securely deleted before doing so. I have carried out the Full Reinstallation option within Settings but I am not convinced that this has erased my files to the extent that they could not be easily recovered by a third party (I suspect they are just marked as deleted as they would be on a PC hard disk). I there a way I could erase files from the hard disk securely, perhaps using a PC utility such as Heidi Eraser?

Wammer.