Hey all, not a huge computer person but I read a few of these threads because I too had the s-video hook up problem.
I believe I found a solution that's easier than re installing 3 times, uninstalling, etc.
I have... or rather should say *had* NVIDIA Geforce 7 that was accessible through the control panel when I had Vista. Of course after reading some forums seeing that people were experiencing problems I tried to follow along and discovered that no where was my NVIDIA installed. Windows 7 didnt report any errors or that the drivers werent compatible and I updated right before my switch to Windows 7 so I don't know what happened to it.
My solution was as easy as going to the NVIDIA site and downloading/installing my driver again, reboot, worked. Had to mess with the NVIDIA control panel a bit (looked like I was in 400x600 or close to it until I set my laptop to be the main screen) but S-Video works!!
NVIDIA owners will probably find this solution helpful since it looks like they have a bunch of beta builds for Windows 7 users for most of their cards. They must've had some feedback because they are beta and Windows 7 specific.
Hope this helps someone out there. Cheers.
Also: I should add that before installing my driver again I did not have any options in the display panel-there was number 1, my laptop screen. After installing the NVIDIA driver, I used the NVIDIA control panel versus the windows display options. May help.