Tim,

I should have been a bit clearer. There was a known issue with importing AC3 audio streams in MPEG2 files in 8.0a. I would add media to the timeline and get video but no sound. This was fixed in 8.0b.

However, I notice on my work dekstop installation of Vegas if I render out audio only to an .AC3 file, I can't then seem to re-import it (which seems slightly bizarre). I'll do some further checking.