mplayer has trouble reading a lot of DVD menus in my experience, even with libdecss installed.
I recommend using Ogle to watch DVD's.
If playback still sucks, you might have to enable DMA (assuming that hdc is your DVD drive):
First verify that DMA is turned off:
$ sudo hdparm /dev/hdc
If using_dma = 0 (off), then enable DMA:
$ sudo hdparm -d1 /dev/hdc
To enable DMA at bootup, open /etc/hdparm.conf and add the following lines to the end of the file:
Code:
/dev/hdc {
dma = on
}