You need to enable DMA on your dvd drive. For example, if your dvd drive is hdc:

hdparm -v /dev/hdc

will tell you if DMA is on.

hdparm -d 1 /dev/hdc

will turn on DMA.

To enable DMA at boot time:

apt-get install hwtools

kwrite /etc/init.d/hwtools

Add this line just above "true" under "hdparm optimization":

hdparm -d 1 /dev/hdc

The above command will then be run to turn on DMA during boot up. There is probably a better way to turn on at boot time, but the above works.