But first, a quick jargon lesson. CPU is not the computer itself, but a part of the computer. If compared to human anatomy, it would be the brain of the computer, which coordinates everything. While the brain in a human is very important, it would be incorrect to use the words "brain" and "person" interchangeably.
That aside, you've got two methods at your disposal. One is cheaper, the other is a bit easier and safer.
Method #1: Extract the old HDD, and install it as a slave in a different computer. Be sure to change the jumper settings so it is set to slave. While fairly simple to do, there is always a small chance of introducing a static shock to the internal components. Simply keeping one hand, or part of your body, touching the metal side of your computer case should keep you grounded, and eliminate this risk. The rest is being able to use a screwdriver (some cases don't even need that), and being able to plug in two cables to the back of the drive.
Method #2: Extract the old HDD, buy an external enclosure for it, stick the drive in the external enclosure, and connect it to any USB port on another computer. Costs more, but there's less risk to the new "host" computer.
Just remember when handling the old drive, not to touch the exposed circuit board on the bottom. You should also avoid any unnecessary jolts, such as dropping it on the ground.
Finally, I'd get a second opinion on the system from someone besides Best Buy's geek squad. While some of those people do indeed know what they're doing, probably an equal or greater number do not. There may be a quick and easy fix someone more qualified could find.
The motherboard on my 3 year old e-machine died (geek squad says it looks like a defective motherboard)...anyways - they tried my hard drive and says that it works and I could use the hard drive on my new computer. It's Windows XP - and my new computer is XP, but I'm afraid I'll do something wrong and wreck the new computer. I'm guessing that I couldn't use one of my old laptops (windows 98 and 2000) to get the data from the old hard drive? I don't have much important info on the old drive - so I don't want to spend the money on having someone do it for me. But, if I decide to hook the old hard drive into my new computer is it really that easy as hooking up master and slave lines? And I read that I might need a power adapter for the old drive...Any other suggestions? Thanks.