If you can hear audio formats OK, but not video formats, then it sounds like 3rd party codecs may be involved and not decoding the audio to Vegas' liking. Do you have a codec pack or ffdshow installed?
Or maybe you simply have the audio volume turned down or muted on your audio track or mixing console or master bus.
I use Fraps, thats where the audio comes from, when I check raw files the sound is there, but when trying to edit in Vegas Pro I only hear it when it's renderred.
Can you delete both of your current comments and start a new topic in the Vegas Movie Studio (Platinum version of which you probably have) section of the forum telling us which template you are using to render.
'TrafficProducer', you don't have to post comments several times. agree with vkmast - please don't hijack other people's thread. Please start new one. Thank you for your understanding.