My email, and answer from ATI:
Graphics Driver Developers
I'm very dissappointed that there is no support for vdpau (or similar) for your gpu's in f.eks XBMC. I just bought a ATI HD card, but it now turns out to be a was a waste of money. I can't play h264 files with any hardware support from the gpu. Fortunately the card was cheap. I have always gone for ATI cards, but in the future will go for Nvidia if you don't go for open source code and let developers take advantage of the potential in the gpu.
DEVREL (10/01/2009 1:16 PM)
No plans to support it now or in the foreseeable future as there was no interest from selected ISVís working on such projects.