How do I get the download from the itunes store to my ipod?

How download Discovery Channel HD, update from iMac to my iPad 2. I can't click on Icon it says 'downloaded'-grayed out!
Fred

Before you can download from the iTunes Store, you must have an iTunes Store account.

To open an iTunes Store account, you must provide a valid payment method, such as a credit card, and a valid billing address. The iTunes Store is not available in all countries. To open an account, your payment method and billing address must be from same country as the iTunes Store you use.


To create an iTunes Store account, follow these instructions:
Note: If you have an Apple ID or MobileMe account, please skip to the next set of instructions.

1. Open iTunes (If you do not have iTunes, you can download iTunes).
2. Choose Store > Create Account.
3. Read through the Terms & Conditions, check the box if you agree to the terms, then click Continue.
4. Complete the form to create your free Apple ID (the login you will use with the iTunes Store).
5. Provide a valid payment method and billing address.
6. Begin shopping from the iTunes Store.

1. Open iTunes (If you do not have iTunes, you can download iTunes).
2. Choose Store > Sign In.
3. Enter your MobileMe account or Apple ID, then click the Sign In button.
4. You will receive a message stating that the ID you have entered has not been used on the iTunes Store before, click the Review button.
5. Read through the Terms & Conditions, check the box if you agree to the terms, then click Continue.
6. Provide a valid payment method and billing address.
7. Begin shopping from the iTunes Store.