On the back of your the drive that came with your system, you have to move
the jumper or jumpers , little plastic pieces (sometimes more than one
jumper is used) that fit over some vertical metal pieces, right next to your
drive's power plug) to the "Master Device on a Cable with 2 IDE Devices"
position. Then on the same flat data cable that's plugged into your Master
drive, you'll see another plug, to plug into your new Slave hard drive (make
sure that the red strip on edge of the data cable is on the same side as
with the original drive. Then set the jumper or jumpers on the second drive
(the Slave drive) to the Slave drive position as indicated in the
documentation that came with THAT drive. Then plug in a power cord to that
drive (your system should have extra power plugs that aren't plugged into
anything. You probably won't have any problem finding the jumper settings
for setting the new hard drive as a Slave drive in its documentation. But,
you might not have the original documentation for the drive that came with
your system to be able to set it to the "Master Device on a Cable with 2 IDE
Devices" position. If that's the case go to the Compaq site and find the
specs for the hard drive that came with the system, which will have the
Jumper settings. Sometimes the jumper settings are on a label on the top of
the hard drive itself. Tip: Tweezers make for a good tool for easily
moving those small Jumpers. Once the above is done properly, when you
reboot, the Compaq will recognize the new drive, and ask you to press a key
like F1 to accept the finding of the new slave drive. Then the boot will
continue into Widows XP. After Windows XP loads, right click My Computer,
left click Manage, and the Computer Management window will open. In the
left pane click on Disk Management, and you'll see your drives in the right
pane. In that right pane, right click the new drive, and you can Format it,
and/or partition it, and/or change the drive letter etc...