Fdisking and formatting a disk are not sufficient to erase data from a disk. Microsoft fdisk only overwrites the first cylinder leaving everything else untouched. Formatting is going to overwrite some spaces with the filesystem metadata but also leaves most space untouched. To erase a disk, you must overwrite the entire thing. On Linux, you'd copy /dev/zero to your drive with the dd program. Maybe you should boot off a Linux CD and erase your hard drive that way.

Without destructive erasing, programs like Lazarus in The Coroner's Toolkit can still retrieve your data. TCT is targetted to UNIX but Lazarus works perfectly fine on Windows filesystems (I've used it on NTFS).