[kosmiq]

Um you just pop it into your DVD-reader (in the xbox), and press "DVD" or whatever it shows up as in your dashboard.
What dashboard are you using btw?

If you are using XBMC as dash and everything go get DVDX, open the xboxmediacenter.xml, edit the line that says "<DVDplayer></DVDplayer>"
to "<DVDplayer>E:\Apps\DVDX</DVDplayer>" or where you out DVDX.

If you are using EvolutionX edit the evox.ini file and add this line:
DVDPlayer = "f:\Apps\dvdx\default.xbe"
in the beginning of the ini file (in the [misc] section, also note that the path is mine and you must change it to fit yours).

Almost the same applies to Avalaunch or whatever...
When you've done that pop in the DVD select DVD (menu alternative DVD in EvoX, the Disc in Avalunch and whatever in XBMC). Enjoy the movie...