You may want to first make sure that the BIOS is set right to detect your Hard Drive. The easiest way for you would be to make sure its on auto detect in the BIOS and that you see it listed when the system posts. Also, make sure the jumpers on the hard drive are set right.
You may want to do a fresh install on that system especially if its XP. Sometimes you can have problems putting in a Hard Drive with an OS already installed on it.