Novice computer users, this post is not for you. But if you have intermediate or advanced skills (meaning that you're comfortable poking around a PC's innards), I'd like to recommend a special tool for your PC repair/upgrade/troubleshooting toolkit.
It's a USB-to-IDE/SATA adapter, one that allows you to plug any "naked" hard drive into a USB port. I've owned one of these for a few years, and while I don't use it often, it has saved the day on numerous occasions.
A recent example: My beloved media-center PC was exhibiting the symptoms of hard-drive failure. I knew I had a short window of time in which to rescue some recorded TV shows before the drive was no longer accessible. The PC itself was no longer bootable, but I was able to connect the adapter to the drive, and the drive to my main desktop. Never mind that the failing drive was still screwed inside the media center at the time! (Getting it out would have required major surgery.)
In another instance, I'd replaced the hard drive in a laptop and needed to retrieve some data from the old one--which was now "naked" (i.e. outside the PC, without any kind of enclosure). The adapter effectively turned it into an external USB hard drive, one I could access with like speed and ease.
I'm not saying you should rush out and buy one of these this minute, just that you never know when one will come in handy--especially if you're the tech-support person for friends and family. These adapters usually sell for $20-30; TigerDirect, for example, has a Sabrent USB 2.0 to IDE/SATA adapter for $19.99. It comes with everything you need and works with all drive sizes (2.5-, 3.5-, and 5.25-inch).