Hi !
I have problems with my monitor in version 3.4, I always use this parameter:

knoppix screen=800x600

because I have an old monitor (Samsung Sync Master 3), but with this version of Knoppix I can use only the monitor in 640x480 resolution.
I tried with kernel 2.6 and 2.4 but in both cases is the same, I can't use resolutions upper to 640x480.
I don't have this problem in version 3.3.
Someone can help me please !