Just run the analog outputs from your camera into your soundcard and do a audio capture right on the timeline. Pick an open audio track, hit the record button to arm the track and check your levels, then hit record and it will bring your aduio right on the timeline as it captures.
1) Capture BOTH, render the audio, then delete the original clip.
2) Use a DIFFERENT capture program (such as Scenalyzer)
3) Capture via Analog (run wires from your camera to your sound card) directly to the Vegas timeline.