now it works ok from the last time. In fact i was wrong not using the relative values for 'tv' display. For example :
if you have 1024 x 768 display on your crt
the value indicated in second place in the sentence is representation of the display you want for tv. In the end with a display of 1280x1024 on my crt i set 800x600 for the tv and it builds a relative desktop which represents my crt display.
It could seem very simple but as i'm not english native, sometimes few words could give me the thought i understood and finally i can see i didn't.
For easy setup with mandrake 9.1
first install with the advanced options and especially let the driver find out where are the libraries needed. Add --openg-gl too
a lsmod and a modprobe for the nvidia and everything runs fine