Thanks to all for the replies!
Which connectors do I use on the motoherboard? My first two, 0 & 1, are used for my two existing HD's. The third connector, #3, is used for my CD ROM. And #5 is connected to the media bay in my case.
The drives I want to add are Seagate ST3750640AS Barracuda 750 GB SATA 3.0GB/s Internal SATA II.
Thanks again.