There are a number of programs available for playing dvds on your xbox. I use either xbox media centre or dvd-x2 donglefree dvd player. I don't know if i'm allowed to tell where you can get these programs from, perhaps one of the moderators can advise on this, but try
www.xbox-scene.com for tutorials on how to use these programs. You will also find helpfull tutorials on how to get these files from your pc to your xbox.
Hope this helps.