X and Fluxbox :: How can I change the video driver to use sisfb

I use hd-install to have a hd using dsl.

I tried to change the video driver to use sisfb because the vesa driver is too slow to play video. I changed /etc/sysconfig/xserver and /etc/sysconfig/knoppix for the XMODULE="vesa" to "sisfb".

But everytime I reboot, the file is changed back to vesa again. Question:
How can I change the video driver to use sisfb?

Thanks.

original here.