The problem with TV out on many cards is that they are setup to mainly run as an auxillary or as a "mode" once you have your VGA up and running. Many ATI cards and some Nvidia's will autodetect an RCA/Svideo connection and set the primary display to TV out from boot up. But I am not to familiar with SIS.
I would look and see if the latest PowerStrip utility lets you set the display to video out on startup with the video card. Also if you could build a script or ghosting function that could set the display to output to TV out once in windows you would be set. If you find a cheaper ATI with TV out they sure have great output and features for TV out, wish I had one