ZenBook: Who Is Sitting On "D:" ?

Finally bit the bullet and bought a ZenBook.

Windows 8 isn't quite as traumatic as I was expecting - especially with
the addition of Start8.

I re-partitioned the 500-gig drive into C: System and Z: Data, splitting
the space about fifty-fifty.

What I want, though, is to have that Data partition have the drive
letter D:, but somebody's using the designation "D:" for one of the
drives and I can't figure out how to free it up.

I'm guessing it's one of those un-lettered partitions as shown in this
screen snap of DiscManager: http://tinyurl.com/mv4gofs and Windows 8,
for some reason, isn't showing letters.


Anybody have an idea of how to get to the bottom of this?
--
Pete Cresswell