Apple posted an update for Mac Pros with 10.5.2 and the ATI Radeon HD 2600 XT graphics card on Tuesday. The firmware update improves the system stability, according to Apple.
"This update is for Mac Pro computers with one or more ATI Radeon HD 2600 XT graphics cards installed, running Mac OS X 10.5.2 or later with the Leopard Graphics Update. It updates the ATI Radeon HD 2600 XT graphics card firmware on all of the ATI Radeon HD 2600 XT graphics cards in the Mac Pro to improve system stability. Installing this update on a 2.8 GHz Mac Pro system configured with multiple hard drives or more than 2GB of RAM will result in the system meeting Energy Star 3.0 requirements," the update says.
The update is available via System Preferences -> Software Update or as a standalone update, 792 KB.