Apple's ATI Radeon HD 5870 Works in 2008 Mac Pro
According to Barefeats, Apple's ATI Radeon HD 5870 Graphics Upgrade Kit ($449) for the Mac Pro does indeed work in the 2008 Mac Pro. This is despite the fact that Apple only officially lists the 2009 and 2010 Mac Pros as supported hardware f...
http://www.macrumors.com/2010/08/24/apples-ati-radeon-hd-5870-works-in-2008-mac-pro/