You're getting that message because Windows is unable to play a DVD without installing 3rd-party software (the decoder in this case).
Usually you would get a programme that included a decoder with your DVD drive (Power DVD seems to be quite standard).
You can view a list of free alternatives
here.
If, on the other hand, this is the
only DVD that doesn't work, you have a more serious problem
[ 08-15-2006, 07:48 PM: Message edited by: shamrock_uk ]