Joe,
there might be different issues!
1. burning-method
have you burned your DVD using DVD SP or have you burned it using mac os finder? finder will not create a proper DVD, as it needs to be formatted unsing the UDF-format. finder will burn the disc using mac os HFS-format, so the disc will not be recognised by DVD-player.
2. compatibility-problem
DVD+/-R media has ofter problems on different players, depending on which player you have, especially on older player that´s a big problem.
3. DVD-media
be awared only to use high-quality-media like verbatim or tajo yuden, other media often have problems with the players
4. PCM audio
98% of all DVDs with playback-issues that I´ve seen has PCM audio on it. if you are using DVD+/-R-media they could only handle max. 8Mbit (total max. bitrate) instead of 10.08Mbit given by spec. so you should use dolby AC3-audio instead of PCM (wav/aif), as PCM have 1.5MBit, that´s a lot more.
you see, there are a lot possibilities why a DVD could fail to play.
cheers
danny