You may be running into some of the inconsistencies of intrepid and the new version of vlc.(they both have issues
Have you tried with another player? (anything but totem-gstreamer.
That dma error is sometimes associated with having a 40 wire ide cable with an umda4 capable drive. (sometimes also with udma2 drives
If your dma is set at udma2 or higher I wouldn't worry.
While hdparm isn't of much value you can still ck. your drive settings. (adjust red to match drive, * shows current setting
You could also grep your logs for 'DMA' to see if your being reset to pio mode (bad), for instance
hdparm -i /dev/scd0
grep 'DMA' /var/log/syslog
If you saw something like this it's safe to ignore if you know you have an 80 wire. (I have 80 wire cables but some Udma4 cable drives on 80 wire cables will only run at Udma2 on linux, no real harm
Dec 13 21:06:43 doug-desktop kernel: [ 19.175758] ata1.00: ATAPI: ATAPI DVD A DH20A4P, 9P59, max UDMA/66
Dec 13 21:06:43 doug-desktop kernel: [ 19.175773] ata1.00: limited to UDMA/33 due to 40-wire cable