burnz said:actually, there's a simple solution to your problems.
you shouldn't waste the decoding prowess of the 8600GT.
PowerDVD actually does play x264 .mkv files, you just need to rename the file extension from .mkv to .avi to "trick" PowerDVD to play it. and wala! you now have hardware accelerated h264 playback using PowerDVD and your 8600GT
btw, i used PowerDVD 7.3 to play the .mkv files under both vista x64 and x86, so make sure you have the latest version installed, to be on the safe side.
Really will give it a try.