I'm guessing, but this could be to do with the monitor's 'plug and play' (think for a monitor it's called 'DDC'). I had this sort of problem with a CRT monitor that would support 1280x1024 at 60Hz and also 1152x864 at 85Hz - Knoppix along with other distros chooses the latter setting as it's refresh rate of 85Hz is kinder to the eyes and ignores the higher resolution. The way I got over this was to start to boot Knoppix, enter screen=1280x1024 but before pressing the return, unplug the monitor..... No monitor plugged in, no DDC! When Knoppix has finished booting, plug the monitor back in. (NOT RECOMMENDED).

Very crude and I take NO responsibilty if this fuses your monitor, in my case my CRT monitor was worth about £15, not too much to gamble. I just thought you'd like to know what my thoughts were on this. As I say, this could be completely wrong..... if it is DDC, maybe there is a better way of overiding it?

Stoo.....