Get GSpot.. it's free and it will tell you what you need to play a certain file.. just open the file in GSpot and it will tell you.
http://www.headbands.com/gspot/

Get an xtra backup player with built in codecs: VLC: http://www.videolan.org/vlc/ (choose nearest mirror site & it's free & plays ALL except the odd wmv file!)

Xtra help on dvd burning see: http://www.videohelp.com/ for all sorts of tips & tricks & softw.