I looked a little further on the internet and finally found a solution on the SuSE mailinglists!
A VERY nice genleman had suffered the same problem and tried to find a solution for nine days. He finally found that adding the option
Option "NvAGP" "0" to the XF86Config file
<like so>
Section "Device"
BoardName "GeForce4 MX 440"
BusID "1:0:0"
Driver "nvidia"
Identifier "Device[0]"
Option "NvAGP" "0" <------------------------
Screen 0
VendorName "NVidia"
EndSection
solved the problem. He still has trouble getting in the text consoles though (like, with ctrl-alt-F1), but that's not the case here. Everything _works fine. He has a different nVidia card, perhabs that explains it ???
The point is, he told me that he hasn't got a clue on *how* this works. It seems very counter-intuitive (like in quantum mechanics

, switching *off* AGP, but well ...
See the whole solution on URL:
lists.suse.com/archive/suse-linux-e/2003-Sep/1505.html
thanks, Jan!

WahWah (now going off for a trip to Saturn with Celestia)