Hi Jochen and others
You may try NetBSD.
I looked at *BSD but it seemed to only support the Ultra 1E and not the
Ultra 1. Tried Ubuntu Linux, that died while trying to partition the
disks. Now installing Aurora (a Redhat spinoff), that seems to be
working nicely.
I've run NetBSD on an Ultra 1 without any trouble.
Peace... Sridhar