Things You'll Need
Instructions
Select and purchase your hard drive. Hard drives can be found at virtually any video game/electronics retailer or online. If you're just looking to save games, 20GB should be plenty. But if you're in the market for saving movies, music and photos, as well as downloadable game content from the Xbox LIVE marketplace, then look for a bigger hard drive.
Power off your console and remove all cords and cables from it. You don't want the machine powering on while you're installing the hard drive, and possibly corrupting a file or some hardware.
Lay your Xbox 360 up vertically so that the hard drive bay is facing up. The hard drive bay is the flat area on the top of your Xbox (or to the left of the DVD drive if you have the console lying horizontally), with a small input in the middle.
Slide the hard drive into the hard drive bay, tapered end first, and push it down until it clicks. Now you can plug your Xbox back in and power it on, where the main menu should recognize the hard drive. It's now installed and free to use.