>Ah, what version of NetBSD did you attempt to install?  Older versions
>indeed did not support the powerstorm, but the latest 1.5_ALPHA snapshot
>on ftp.netbsd.org should support it just fine (including X).

Now I did download 1.5 alpha2 from

ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-1.5_ALPHA2/alpha/installation/floppy/

and did boot:

Entering netbsd at 0xfffffc00003010c0...
panic: tga_console(12, 0): unknown board configuration
Stopped at 0xfffffc0000537fc4: ret zero,(ra)


:wq!
RoF