Hello Muaaz17;
How many physical hard disks does your friend have in his computer? 1 or 2?
You probably have 1 hard disk with two logical partitions C: and D:
Disk Partitioning
You can create and manage partition with a program like:
EaseUS Partition Master 9.1 Home Edition
But you need to be very careful and understand what you're doing. A wrong move and you could ruin your current OS installation.