If you are adding a second hard drive, you need to decide which one will be the master and which one will be the slave. The master is your drive C. The other one is the slave. Look at the instructions for the hard drive. It will tell you how to make the drive a master or a slave. They usually come configured as a master, and you simply adjust a jumper on the back of the drive to make it a slave. A later computer can handle two IDE hard drives per IDE channel.
Get the setup in your mind. Which IDE channel? Master or slave? As a consideration, don't put the hard drive on the same channel as your CD-ROM unless you have to.
Physical Installation
Okay, now lets do it. If you are only installing a second hard drive or a new one, you can skip down to step 5, although this might help as a reference.
Remove the cables from the old drive. You will see both a wide IDE ribbon cable and a small 4-pin power plug. Do not force them out. The ribbon cable is usually quite easy to remove. Sometimes, though, the power connector can become stuck. Just rock it back and forth, taking care not to rip the connector off the drive.
Remove the mounting screws that hold the drive to the case frame. Sometimes, you may need to tip the case or get into some strange positions to reach all the screws. But, that's part of the fun.
Slide the new drive in right where the other one came out. If it 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. If you are adding a second drive, just pick any empty drive bay. Screw the drive into place.
Attach the cables to the hard drive.
