This link is outdated and somewhat inaccurate but it covers the basics.
Read EIDE Hard Drive Jumper Settings from http://www.wdc.com/en/library/eide/2579-001037.pdf
A jumper is a small piece of plastic (there can be two jumpers) on the hard drive end, see diagram in the Western Digital link.
On the hard drive itself...is a diagram showing the possible jumper settings.
My advice is to look at the hard drive you already have installed on the system that works. If the jumper on that drive is set to Master and you connect the old hard drive on the same cable...set the jumper on the old drive to reflect Slave. If the jumper on the working system is set to Cable Select/CS, set the jumper on the old hard drive to CS.