DXVA for H.264 and VC-1 videos *doesn't work* under WinXP.Under Windows XP,you need to use a player that uses DXVA to use UVD on Windows.
http://mpc-hc.sourceforge.net/ does, although I have found some H264 broadcast streams that don't work. I don't have a clue if it's the player, DXVA, the drivers or UVD on my card that's the problem. Most H264 seems to work - the ones that didn't were 1088x1920 so maybe that confused things.
I've tried all existing players for Windows (PowerDVD, MPC-HC, KMPlayer, WMP) with all video renderers (Overlay Mixer, VMR7, VMR9, EVR), but nothing works with the Radeon HD 2600
There's no HD video acceleration under WindowsXP for ATI cards.
I don't need BluRay acceleration, I only need video acceleration for normal H.264 videos (free / open-source 1080p HD clips / trailers / videos you can download from the net).
Take the Elephant's Dream 1080p video as an example:
That video is so demanding that it's impossible to play it on a machine with a (relatively powerful*) single core CPU.
* not an Atom or Sempron