The only way I could think of this working (in a manner that would fool a member of the general public who came across your DVD)
Would be (if such a program exists and I'm sure someone must have tried this)
Would be to burn the DVD movie data onto the disc via a program that encrypts/modifies the data as it's writing.
You would then have a DVD which a normal player (or PC) would not be able to display.
Yes, you would be able to copy it, but you could still not play it.
What you would need is the special (custom) playback software, that decoded what the writer had done (in real time) and displayed the data.
Pretty much in the same way that you create a password to scramble an email, and you need the same password to descramble it.
I'm not sure if such a program had been written to do this job, but it's easily possible.
Of course, I'm sure a hacker would manager to decode the data (if it was important enough to spend time on)
But it would definatly stop "average" people from being able to play your DVD's without using the software/password you also provided to decode and view it.
(Just a thought)