Some additional information, I was a bit too fast sending the previous
message:

Christoph Biedl wrote...

> Providing "agp=off" works around the problem, so does "toram" (tested
> for -small only).

* "agp=off" seems to make X unusable for missing /dev/agpart,
  surprise.  I didn't search for workarounds.
* "toram" works for full-size grml, too, and is also a workaround.-
  Having a lot of RAM is probably a good idea for that.
  However, an USB device like a mouse and sound are unusable.

Matches the expected behaviour :)

    Christoph