Hallo Dieter (ich schreibe in Englisch weiter, um besser verstanden zu 
werden) ;)

> Use mesa-dri out of pkgsrc-wip instead of MesaLib, and copy the
> MesaLib.buildlink3.mk file over graphics/MeasLib/buildlink3.mk.  This
> gives you DRI-enabled GL libraries and driver modules.

I've done that.

>   Which major device number does your /dev/dri/card0 use?  What's the
> output of ls -l /dev/dri/card0?  (The major number should be 180; it
> was changed during import.)

I've changed that also. Now I get, at the end of the Xlog, this:

drmOpenDevice: node name is /dev/dri/card0
drmOpenDevice: open result is 8, (OK)
drmOpenByBusid: Searching for BusID pci:0000:01:00.0
drmOpenDevice: node name is /dev/dri/card0
drmOpenDevice: open result is 8, (OK)
drmOpenByBusid: drmOpenMinor returns 8
drmOpenByBusid: drmGetBusid reports pci:0000:01:00.0

which seems okay.

However, when I "startx", the screen blanks out and nothing happens. 
Just a black uniform screen. The system is not hanging, I can still exit 
by CTRL-ALT-BACKSPACE and reboot, so this is no kernel panic or 
whatever, just maybe a problem with the colormap????

Any further hint?
TIA.
Vincent