Most internal parts you can just plug in while the computer is off without any hassles, I have checked a couple of old hard drives out doing this Click here to enlarge There should be two cords you need to plug in, one for power and one for data transfer; basically just put them where they fit (one that should go to a connector coming from the power supply and one on the motherboard, the large circuit board on the bottom). Whether the spots are there for the plugs to go into will depend on whether the computers are from a similar era, as they used to use a different cable for connecting hard drives.

Have never needed to mess around with master/slave drives much, with any luck it'll start as normal and you can access the other drive from My Computer Click here to enlarge

Edit: The 4 pin plug is for power, they can be difficult to plug in but don't be afraid to use some force and do a bit of wiggling. The only other one you should need is the large flat data cable (called a PATA connection I think) and if you have a spare spot on your motherboard just plug it in there and you're good to go Click here to enlarge Just be careful not to bend the pins when you put in this cable and check you have it the right way up