If you are using Vegas 7 or Vegas Pro 8, and the render format matches the MPG files exactly, and you have not change the files in any way with FX, etc., then Vegas will "smart render" the files. This means it will simply copy the input to the output with no loss of quality.
If, however, one of the MPG files doesn't match the output format exactly, or you add FX, or you are using Vegas 6 or below, then Vegas will re-render the files and there will be a quality loss.
~jr
www.johnrofrano.com
www.vasst.com
