The best place to look is within BIOS.
There are various other places you can look as well, such as Device Manager (Right-click My Computer, Left-click Properties) and System Information (Start>Programs>Accessories>System Utilities>System Information).
Or, take the side cover off and physically look at it. The plugs are quite different.
Here is a catalog of some plugs:http://www.alibaba.com/showroom/Sata_plug.html
I hope this helps.