The composite or s-video output included on your video card simply converts and outputs whatever normally appears on your computer monitor to a signal suitable for a NTSC TV or similar analog device. The primary intention of these ports are to allow you to play a computer game which would normally appear on your computer monitor, on a larger TV screen, etc.
Therefore, you couldn't 'configure' MSP6.5 to send previews to the s-video or composite port. You'd configure your Windows 'screen display settings'so that your usual Windows screens appear properly on a device connected to that port. Usually this requires that you adjust your Windows screen display to 800X600, and your horizontal frequency to 60 HZ. This is not the same as 'previewing' your video via your camcorder. You'd see the entire MSP6.5 User Interface on your TV.
PS. The September 2003, Videomaker reviews a video card (Matrox Parhelia, $399) that will provide the function you desire.