To me, the handling of external monitors seems to be a somewhat sad story in Knoppix 6.2.*. In 6.0.1, it seemed as every combination I tried just worked, now it's more like try out and hope for the best, find workarounds as you go. Every PC/screen combination seems to be a little different, I think I have about as many adaptations as use situations now - and they are a few. And for handling this adequately in a permanent install, I would say go Debian (or Ubuntu, in my view basically a Debian derivative) .

In the general case, I have found I have to choose one display at the time, I can't always make it work to switch between them. And, like now, working on a 1920x1200 Benq monitor and an ASUS UL30VT laptop, I had to start Knoppix with the cheat codes no3d screen=1920x1200. That is, drop Compiz, and forget about using the computer screen and the external display interchangably. This is plain VGA, for other outputs I would guess it is even more complicated, and rather hardware-dependent. And because this behavior has changed so much between releases, I haven't thought it worthwhile to dig deeper into it. Going all the way down to hardware detection, initialization and graphics drivers would be necessary, I guess. Otherwise, any working hack found might just be nullified in the next release.