Horkn you should be able to add the old drive on the SATA cable and access it as secondary drive. You will need the new/existing drive as primary since it's running the OS. There are also adaptors that allow you to hook up the old drive via USB, and access the drive easily.
What Chaz said, or buy a usb SATA drive enclosure and you can permanently mount the drive in the case. Amazon - ineo 2.5" USB 3.0 Tool-Less External Hard Drive Enclosure
The cable probably won't work, since it's a platter drive. Prolly need a power source, so either put it in the case, or get an external enclosure. Oops, just noticed the box says power included. Never mind. SSDs can use a non-powered cable. Makes for an awesome external, portable drive setup.