ATI official
Despite previous reports on the internet that old Radeon 38×0 and new Radeon 48×0 cards will work in Crossfire together, unfortunately this won't happen.
Two senior software guys at ATI has just confirmed that 3800 series in Crossfire with 4800 won't work and that such a configuration is not supported.
You won't be able to match the generations and we are investigating if you will be able to mix cards from 48×0 series. We believe you should, but we won’t jump the gun with this announcement.
Sorry for destroying one cool dream, but you will have to forget about your 38×0 card and swap it for a much faster 48×0 generation.
At the same time, our friend W1zzard from tech power up has confirmed that he couldn't make 3800 and 4800 generation cards work together in XP, but now we know the answer why. It won't work on XP or Vista, simply as it's not supported.
