OpenBSD's website (click here
) says that it's actively ported/maintained on the PowerPC architecture, including the PowerBook G3/G4 and iBook. Be warned though - OpenBSD is not
Linux. It is also a UN*X based OS, but it is not Linux.
As mentioned above, I'm not a Mac person, but if the PowerBook arch. is the same as the PowerPC (PPC) then most distrubutions should
work OK. I know that Mandrake 7.2 (the version I use) can be installed on one. With only 400Mb of HD space, you are probably a bit pushed to what you can do.
The basic X Window System (or X, X11, etc) normally takes up about 120Mb, and that's without any programs!
If you have another system that's got a larger HD (Mac or IBM compatible), I would suggest that you install it on that instead. Although the system itself is capable
of running Linux, the easiest part to use is definately X (with either KDE or Gnome) and this is what many newbies see as the OS.
If you're not worried about messing things up, by all means give it a go on your PowerBook! There's not much you can do by way of 'breaking' it that is beyond repair!
Have fun, and don't give up if it seems a little daunting at times - it'll be worth it!