I don't know of a guide to link you to, but if you're using the classic control panel, then after your TV is connected to your video card via S-video, change your TV mode to Svideo input, and on your computer go to your display properties.
From there, go to the settings tab, then click advanced, then go to the 6600GT tab. There should be a new window with graphics settings...the first of which is nView Display Settings. Go there, and under nView display mode, choose Dual View and apply. Alternately, you can try clone and see which you like better. It should automatically pick up your TV and begin displaying to it.
You can play with resolution and what not afterwards. Hope that gets you going!