ok most users know this or some probably dont.
vista home premium and windows vista ultimate come with a buildin dvd decoder.
For those who are running Windows Vista Home Basic and Windows Vista Business,you can download the following dvd decoder below which works nice =) since i use it aswell. XP users can use this aswell since this should work for them aswell.
Its called VLC - look into it. Plays DVDs, CDs, xvid, divx, mkv, anything really.
Works with Vista. Problem solved.
Download Here >
http://www.videolan.org/vlc/