D: is another physical drive.
I recently had a problem with my computer, before this problem, that forced me to buy another harddrive or reformat my harddrive which has important data. drive C: is supposed to be two harddrives that equal up to 320 gb, im assuming thats what you mean by partition, however that drive is currently only reading one of the 160 gb harddrives. so to sum it up, drive c: is supposed to be 320 gb, but is only being read as 160 gb. c: is the drive windows is installed on, c: is the drive that im having problems with.
also, I feel uncomfortable taking things in and out of my physical computer, because im afraid ill either break something or place it in wrong. I have no knowledge of how to replace harddrives.