Try knoppix xvrefresh=60 screen=1024x768 and you may want to put the xmodule=?? cheat code for your video card on the line as well.
60 is not the correct value; just like 5thelephant, I have tried several with no joy.
I don't actually have a video card.
Or a sound card either, I have that insane shared memory all-in-one processing on the motherboard, which I suspect is part of the problem.
I do know it uses the Sis 630 chip, but I've no idea which module to tell it to use.