I am having the same problem with Knoppix 4 and a Dell Latitude D610 with Intel 915 video. Text mode works fine for me, but when X loads, my screen goes blank. Ctrl-Alt-F1 through Ctrl-Alt-F4 change contexts ok, and I can use the command-line interface ok. Params that do not fix the problem:

fb1400x1050
fb1280x1024
fb1024x768
fb800x600
screen=1400x1050
screen=1280x1024
screen=1024x768
screen=800x600
noapci
noacpi
acpi=off
nodma
hwdetect=off