[CrazyN8]

How old is this computer?

Take the case off your computer.....find the HDD (it should be the one that doesn't exit the case (have an access point from outside the case).....look at the ribbon that connects it to the motherboard.

Is it about 3'' wide (IDE) or is it about 1/2'' wide (SATA)? If it is really wide all you need to do is find a spot on it to attach the other drive or get another IDE ribbon that has two spots on it for drives and attach the other drive. I can't imagine you not being able to add another drive. If it's SATA look on the motherboard where the other drive connects and see if there is a place for another cable like that to attach.