Apple Finally Acknowledges and Addresses ATI X1900 XT Issue
Apple recently posted a support document acknowledging an issue with ATI X1900 XT graphics cards that shipped with Mac Pro systems between August 2006 and January 2008. (via ZDnet and forums )
If your Mac Pro experiences distorted video and has an ATI X1900 XT card in it, you will need to bring your computer's serial number and the graphics card itself into an Apple Authorized Service Provider or an Apple Retail Store location for verification and to exchange the affected graphics card for a new one. Affected graphics cards have "V6Z" in the last part of the card's serial number.
This program covers affected ATI X1900 XT video cards three years from the original date of purchase or until January 31, 2011, whichever provides longer coverage. The ATI X1900 XT issues have been well documented and the subject of many support discussions on our forums and others. So, if you are affected and can dig up your old graphics card, Apple has an exchange or refund waiting for you.