If I were you, I would get more RAM for this machine (check auction sites) and run MkLinux DR3 or RC1. I think that it is one of the only Linux ports out there that really supports the PB 1400 old architecture.
As already pointed out, there is a kernel port for nubus macs. I'm running debian on a pb 5300 with grayscale screen (but with 56 megs of ram).
To install debian (or any other major linux ppc kernel based distribution) use one of the install disk image on the nubus site (they have been modified to boot with the nubus kernel).
Y --
