I use the DOD overwrite function in Recuva to remove the possibility of file recovery for security purposes.
This software could be absolutely outstanding by having it destroy the files reported to be in the
Windows XP MFT and "not able to be overwritten" and also having it delete any zero byte files it finds when doing the initial "overwrite" process.

It does not appear to be possible to overwrite file info in the MFT, apart from workarounds such as allocating enough new zero-byte files with dummy names to fill the deleted entries and then deleting them (as cleanup software does).