#1 hit Google and search for web sites documenting S-Video support or hack
#2 hack your console if it doesn't support S-Video.

AFAIK TG-16 doesn't have S-Video support but it does have RGB somewhere so you should be able to make RGB to S-Video adapter. Genesis may have S-Video support but I'll have to open up and see what kind of chip it has. I don't think Genesis 3 can have S-Video or RGB as it was built as cheaply as possible. (It doesn't support PBC, 32X, or Sega CD either so why bother)

Update, (http://labwww.csv.cmich.edu/luke/vid...sCD32X/svideo/) Genesis 1 can have S-Video but Genny 2 and 32X can't so you'll have to make RGB to S-Video adapter as well.

www.gamesx.com covers a lot of the video mods. if it's not there then either it's not well documented, not popular, or no one's tried to make a mod yet.

Beside Genesis and TG-16, NES doesn't have S-Video support and it doesn't have RGB capability either! Odyssey, Intellivision (all versions), SMS (both versions) and Colecovision don't have RGB or S-Video support. :P