Vegas is an NLE (non linear editor). While technically any computer editor is an "NLE", few get the outright label. Most are just called "editors".
All NLE's can only input and re-encode output.
What you want is a simple MPEG EDITOR.
And to expand on that, what you want to do it mere splicing (think digital scissors/tape). Not really "editing" by normal usage either.
MPEG editors can splice WITHOUT any re-encoding required. It re-encodes the GOP where the cut is located (about 15 frames) and that's it. The rest of the file is untouched. Some can even add simple fades/transitions at the cut (that few seconds is also re-encoded as needed).
No MPEG editor is perfect. Keep this in mind. Certain MPEG files will lose audio sync on certain editors.
I use Womble MPEG-VCR a lot. I use my JVC DVD recorder as an MPEG capture device, than use the Womble tool to cut out unneeded stuff at the beginning, end, etc.
Don't let the weenie website design fool you. This is a powerful tool, and very popular. It has a 30-day trial, and is very well priced.
And then follow this guide:
... and even though it says "removing commercials" it's really just a quick guide on how to remove unwanted footage from an MPEG file.
Another new option is VideoRedo.
This is suggested for Hauppauge capture card users.
Hauppauge files tend to lose sync easily.
That one can be found at www.videoredo.com
Womble also makes MPEG Video Wizard.
Just be aware tha MVW will convert audio to MP2 by default.
It does not cut AC3 (at least not in the version I have).
Also available at www.womble.com
All of these have trials too. Some are 15 day, some 30 day.