Re: Adding a hard drive
If you are putting it on the same IDE cable as the other, you might have to make it a slave. Look for jumpers on the back. As long as you don't pin it as master and have the other drive as master as well, it should just show up on your computer as another drive with data on it. The only real reason to reformat it would be to reclaim the space the OS loaded onto that drive is taking up.
You could get fancy, and have a dual boot system where your pc can boot either the current hard drive, or this drive, but that's a little more involved. For now, just plug it in, and boot up. As long as you don't touch your current drive, it should just show up as extra space.