Install XP to C: installs on C: & D: whack'n all data on D:

Strange this:
Installed XP Pro on a SCSI X-15 Cheetah with no apparent
problems until I looked at the drives in the Disk
Management Console (DMC) where, to my amazement, I saw

C: drive listed as: Healthy(system)
D: drive listed as: Healthy(Boot)

Investigating further I found they were both identically
populated as if D: may have somehow been a mirror of C:
but with no RAID exist on the system; it was a clean
install. Selecting one drive in the DMC picked both; they
acted like the same drive. Trying to recover the data lost
on D: with data recovery software produced gibberish files
that didn't mean anything, least to me. After sending a
log file to a recovery vendor: stumped them as well.
Showed them the files I supposedly recovered: they had
never seen anything like that before. I'm thinking I can't
be the only guy on the planet had this happen or at least
seems like a real someone (a fast-gun maybe) would at
least understand what may have happened. So far, can't
seem to find anyone. Thought I'd try posting here to see
what happens. Maybe someone knows or has some ideas
anyway. Thanks!
~Larry