What version of Vegas are you using? Do you know how the audio was encoded?
I happen to have an MPEG-1 file lying around that I used in a project this morning. It was from a VCD I created many years ago. Vegas shows the audio as 44,100 Hz, Stereo, MPEG Layer 2. I'm playing it right now, over the network, on the Vegas 6.0d timeline. It's an old video of Bob Dylan singing "Tangled Up in Blue." Taken when Dylan was in his prime in the mid-1960s. Before his accident and before electric. He was an amazing force at that point in time. Awesome performance. I get goose-bumps every time I watch it.