In the next week or so, the iTunes Music Store will sell its 100 millionth music download. To celebrate, Apple is giving away prizes including iPods, free music and a super-sized PowerBook.

To enter the contest, you simply buy a song from the iTunes store.

Or... you could enter the contest free!

As noted by Engadget, the iTunes 100 million song contest has a "no purchase necessary" option.

All you need is iTunes, which you can download for free here from Apple for Mac or PC. If you have it already, make sure you have the latest version (4.6) – usually when you start iTunes and it’ll tell you if there’s an update. Then, simply click "Music Store" and click any album, song or whatever, and click the “Tell a Friend” button.

Instead of telling a friend, put in the following email address: itunes100@apple.com. Click send and you’re entered.

If you have iTunes, you can just click on this link to launch iTunes and start the process. Select the "Tell a Friend" button and enter itunes100@apple.com as the address.

Note: Entrants must be 13 years of age or older, and a legal resident of one of the 50 United States, including Washington, D.C., the United Kingdom, France or Germany. Entrants must enter the Promotion through the iTunes Music Store accessible in your country of residence.