I changed xorg.conf.new like that :
Option "NoAccel" "True"
and nothing else then a screen appeared, but only the cursor will peep out.
Then I tried xdm -config xorg.conf.new,
and xdm appear, but do not accept a connection with a regular user nor root.
My usb mouse acceleration also was wrong.
Something elses in someone's sleeve ? How to know, once and for good, if my graphical card
has driver available for itself or not ?