Here's the hard drive transfer disc for the 360. Comes with the 120GB HD to transfer all existing data (Games, Profiles, Music, etc...) from one hard drive to another.
You'll need the data transfer cable to use this disc. Here's how to do it:
1. Make sure your existing hard drive is attached to the side of your Xbox 360.
2. Plug the data transfer cable into your new HDD that your transferring the data to. (Only one plug will fit the HDD)
3. Plug the other end of the cable into the back of your 360. (That plug will only fit one place)
4. Insert the disc and follow the directions.
It will wipe your existing hard drive clean and transfer everything to the new one.