hello,
i was having a sort of similar problem, and tried morien's suggestion but it didn't work.
the video is divx 5 and the sound is VBR mp3 @ 256 kbps. the video works fine in xbmp, but there is no sound at all, it works fine on my computer though. i checked the file in vdub, and it said that the "mp3 vbr headers" or something were messed up. it said i could change them to cbr headers, but it might make the audio off-sync. i went ahead and tried it, and indeed, the audio was offsync. i then tried the stuff that morien suggested, but when i add the wav file, the audio is still off-sync! the original file is still ok, i saved it with the re-written cbr headers under a different name. i am totally stumped to why this is happening, as the video works fine on my computer. any ideas?