Mount Hard Drive

Before simply following the directions below on mounting the hard drive, pay attention to where you put it. Technically, you can put the hard drive in any free bay of your case, but there are a few considerations. Hard drives generate heat, especially the newer 7200 and 10000 RPM drives. Therefore, it is best to place these drive as far from other hardware as possible. Give them room to breathe. If it is necessary to install a drive cooler, make sure you have room. Also, some cases give room under the power supply to install a hard drive. Bad idea. A power supply is like a magnet, and magnets and your data do not go together. Don't install a hard drive anywhere near the power supply. Keep your hard drive near the front of the case.

That said, move on:

Slide the hard drive into an available drive rail of the case. All cases have a space (maybe two) for a hard drive that is below the floppy drive bay and has no access to the front of the case. This is fine, since who needs to see their hard drive from the front? If the drive is smaller than the drive bay (if you are installing a 3.5" drive into a 5.25" drive bay), you may need to add rails or a mounting bracket to make it fit (these are included with most hard drives). Screw the drive into place, making sure not to force anything. And, uuhh, power connectors face the back. Good!

In some cases, tightening down screws on the far side of the hard drive can be a problem, because the screws are not highly visible and thus it is hard to get to them with a screwdriver. It can take a little creativity to get at them. Most cases which have this problem have little holes where you can stick the screwdriver through and tighten the screw beneath. If the screw is not in there, I’ve even had to do a controlled fall of the screw onto the hole and then use the screwdriver to position it into the hole. It’s a pain in the ass. If you have a magnetic screwdriver that can hold the screw, this might be less of a problem.
Repeat Step 1 for any slave drives you might be installing.
To double-check, you should have an installed hard drive, securely fastened. The power lead is connected and the IDE ribbon cable leads from the IDE 1 connector on the motherboard to the IDE connection on the hard drive itself.
SCSI Drives
If you are opting for a SCSI drive setup, then there are a few minor variations from the procedure above. First, you need to install a SCSI controller into one of your expansion slots (unless your motherboard has an integrated SCSI controller). Then proceed:

You need to set any switches or jumpers that need setting on the new drive. In SCSI setups, each device gets its own SCSI ID, numbered 1-7. #7 is usually given to the adapter card. You may pick, then, any other unused address. You may need to take into account any little quirks in your adapter, such as special likings to other addresses that could cause problems a little later. You'll need the manual for this one.
Check for the correct termination. In SCSI setups, the adapter can hold up to seven SCSI devices. These devices are hooked up in a chain, usually with the adapter at one end and another device at the other end. This ending device must be set to be the terminating device, therefore ending the SCSI chain and making a complete electric curcuit. In some cases, the adapter is in the middle of the chain, therefore you must terminate at both ends of the chain. You may need to consult the manual for any special termination techniques particular to your brand of drive. In general, a certain jumper setting will enable internal termination on the drive itself, eliminating the need for a special terminating plug.
Slide the drive in and connect the cables. Make sure that pin #1 on the ribbon matches up with pin #1 on the drive. Yada yada…same as above.
When performing this physical installation, you'll find that it differs from case to case. With some cases, the drive rack is simply part of the case. With this setup, you simply push the drive into the case and screw it in. In other cases, the drive rack may be removable. Some have many separate racks, and some have one removable rack that can hold many drives. With this setup, remove the drive rack. This is usually done by squeezing two metal tabs together to release it, or you might need to use a screwdriver. Then slide the rack out. Screw the drive into the rack per above. Then, slide the rack back into place where it was.

When you are done, you should have a hard drive properly screwed into the case and the ribbon cable attaching it to the IDE controller and the power cable attached.