In the VERY few instances that Nero does not play the sound I either use a player called Quicktime Alternative (which is Mediaplayer Classic with some codecs that Nero does not have) or VLC Mediaplayer. I would try VLC. (link below). I have not been able to burn those to DVD-format with sound, but I haven't really tried since I just connect my PC to my TV and Stereo. If you have a fairly new computer and TV that should not be a problem. They all have some kind of video in/out. I use S-video since I have that in both.

www.videolan.org

BTW Nero7 has a (new?) update out. Haven't got around to getting it yet but it may solve your problem.