Okay, did you install them yourself?
To see if you've got them on different partitions (which I think you do becuase of the option on boot-up) once you're in Windows, go to Start -> My Computer -> See how many drives you have
If you've got 2, and you've only got 1 hard drive, that means that your hard drive is partitioned. Basically, if you have more drives than you do hard drives, it means that your hard drive(s) are partitioned. And by drives, I'm not signifying the CD drives and the Floppy drives etc..