You can print your gift certificate directly from your iTunes Store purchase history. Here's how:
1) Make sure you have the latest version of iTunes. You can download it free of charge:
http://www.itunes.com/download
Note: Installing the latest version of iTunes will not affect your library or any items in your account that you haven't downloaded.
2) Click this link to open iTunes and view your Apple Account Information page:
http://phobos.apple.com/accountSummary
3) Sign in to the iTunes Store using your account name and password.
4) On the Apple Account Information page, click the Purchase History button.
5) Click the arrow to the left of the printable gift certificate you purchased. In the detail section you will see the option to print the gift certificate on your desktop printer. (Note that gift certificates that are sent via email may not be printed.)
If you are unable to print the gift certificate, you can send the code and redemption instructions to your recipient via email. If your recipient is unable to receive email, you could also write the code and instructions on a piece of paper and give it to him or her. Note: Please do not follow these instructions personally, as you will redeem the gift certificate to your own account.