You made it sound like 8xxx and 9xxx series didn't support S-Video at all. But yeah, for some reason you can't configure overscan anymore. You can do several things:
- buy a used 6xxx or 7xxx card on eBay;
- change your CRT TV for a flat screen (I don't know how big your TV is, but 20-22" widescreen LCD displays aren't that expensive anymore);
- use software scaling to compensate for overscan: with mplayer, I found out by trial and error the dimensions I needed to scale movies to, so that they would fill the whole screen without leaving much of the image off: mplayer -vf scale=912:520,dsize=912:520 -nofs for widescreen movies, for instance.