By the way I've noticed the same extra border around the TV-Out on a Toshiba M45 laptop with its S-Video connector. Theres a huge convenience factor with such output from a laptop however the quality is very low!
I've had a little better luck using a TView Micro by Focus enhancements, which simply takes your VGA out and converts it to composite. That gives the expected full screen output and I drive it at 1024x768 and let it deal with converting all that information to the best possible for composite.
Granted thats still an inexpensive product. Our public access TV center here has an Extron VSC 200 Computer To Video Scan Convereter rack mounted with all their other equipment, and I could probably run a 25foot VGA cable from my computer to it as the next step up. This would just replace my inexpensive TView Micro.
The ultimate approach would be the NVIDIA Quadro FX based SDI cards, as pe1chl was hinting at to get the true RGB YPbPr output, pixel for pixel matched for broadcasting for routing through the video switching equipment. Much more expensive.
Which public access provider are you with? At some level, producers from your establishment and ours should keep in touch on such approaches. And particularly, management from each should know how other outfits are addressing this. The public access station I'm at as a producer is http://www.mnn.org/
in New York