>I wanted to update from my old PB12 to the latest release. [...]
>m0n0wall doesn't work properly afterwards.

Rudi, do you (or Chad) happen to be using bridging? I found the solution to
my DNS problem after upgrading to pb20 as described here:
http://m0n0.ch/wall/list/?action=show_msg&actionargs[]=15&actionargs[]=13
and in subsequent messages on that thread, in particular the response by
Manual here:
http://m0n0.ch/wall/list/?action=show_msg&actionargs[]=15&actionargs[]=18

Hope this helps....

cheers, michael