DVD playback under F8 fails - need troubleshooting help

[tom]

I am confused here. I have a fresh F8 install on a Celeron 1.8 based 
system which declines to play dvds placed into the system dvd drive. The 
livna repository is also installed by rpm, and provides the multimedia 
software.  Running mplayer from the command line gives an error message 
from libdvdread (think I got that spelled right) with an assertion failure. 
gxine, xine, vlc, and (of course) Totem all fail to play also.

What irritates me is that a different machine with F8 runs the dvd 
playback just fine.

Any bright ideas of where to start looking (systematically looking this 
time).

Thanks for the assistance