usb-to-serial port cleanup

I have replaced my old USB-to-Serial cable that died with a new one, but
now I can't reset the COM ports for the new device because the
registry/driver settings for the old one are maintaining their
"reservations".

I can't get the old one to be recognized (which is why it needed to be
replaced) so I can remap the old reservations out of the way, and I
can't delete the entries in the registry (security issues).

Any solution to purging this old crap out of the system, other than
reinstalling Vista?