Finally got around to installing a distro on my target hardware...
I installed Ubuntu for something to play with, then installed the OpenChrome driver, and got dri, gl, xv, and 800x480 working. Mplayer play's DVD's (using xv) using about 50% CPU or less.
So far its running stable, no problems. I just had to make sure the video apps are using xv for the output driver. I havn't attempted to try getting mplayer to compile with the OpenChrome patch for xvmc (would that lower cpu util enough to matter?)