For watching a dvd - make sure you have dma enabled for the dvd drive.
Here is an article about your chipset:
there is a link to a driver page.
However, you should check that there isn't already a driver package specifically for Mepis/Debian. (It is very likely there is one, and very unlikely that you will have to compile anything. Have fun.)
If you installed mepis for games/multimedia support out of the box, I'm looking at a spanish distro "LinEx" and it's home/school version "Extreme Linux".
(spanish - the english page is: http://www.linex.org/linex2/linex/ingles/index_ing.html