lsmod and dmesg | more, check to make sure DRI is loaded, and its optional actually, some video setups do fine without it, it is needed for 3D openGL acceleration though. If lsmod and dmesg dont shed any light check xorg.0.log in /var/log and see what it shows. Also open up xorg.conf and check to see if glx and/or dri are uncommented so they get loaded when X is started. What video card are you using, and what kernel?
ya, if the -dvd-device option is working, just make a symlink to dvd like:
ln -s /dev/hdx dvd
sidenote: some motherboards still dont have proper northbridge and southbridge drivers like the via based ones used in the itx mobo's and some socket A's--------I have one of these. Which means the agpgart driver wont load without lots of work to the system compiling and installing some open source third party kernel modules. It also means no DRI or GLX support w/o doing some more compiling and installing including having a built X tree to compile against(aaaaaaaaaaarrrghhh).
As far as whats needed to play dvd's: mplayer, mpeg libraries, libdvdcss,libdvdread------I think thats it, it will even work using the svga library in console mode with 99% of the video cards out there.
methinks we can fix your issues, just might take some trial and error and some more digging for info that helps figure out whats up
