To use cable select, look for are the letters "C" and "S". If the jumper doesn't already link pins with these two letters together, pull the jumper (fingernails can easily do the job) and reset it to cover the "C" and "S" pins, in any order.

What this does is set the drive to "Cable Select," so that how the computer will see the drive depends on which part of the IDE cable is connected to the drive. There should be a second connector on the same IDE cable to which the computer's hard drive is already connected. This second connector is grey in colour and is for the secondary drive. Since the computer's drive is set for Cable Select, just attach this connector to the old drive and the computer will see it as the secondary drive.