In a recent support note, Apple offers to replace certain, problem ATI X1900 XT video cards found in a range of older Mac Pros. Users had complained for several years of distorted video from the cards.
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. See below for details.
Note: If your Mac Pro has an ATI X1900 XT card but is not exhibiting any signs of distorted video, you do not need to exchange it.
Apple didn't detail what card would be provided with the swap. In addition, the company said the exchange 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."