@ AmigaBruno
OS4 won't work. Moana is hard-coded to require PowerMac10,2 hardware, which corresponds to the Mac Mini G4 "silent update" (1.33GHz and 1.5GHz machines only). Besides, it's an old, buggy, beta version of OS4. The kernel and drivers are incomplete, barely work and will never be updated. If you want to try it on your Quicksilver, I suggest not spending more time on it other than to see "Well, that didn't work" after the initial boot attempt.
EDIT: And to actually talk about some things your Quicksilver *can* do: I would suggest triple-booting MorphOS, OSX 10.4, and OSX 10.5 (10.6 requires x86).
10.4 is the last version of OSX to support "classic" emulation, meaning you can run programs requiring MacOS 9 and lower - opens up a big back catalog of software.
10.5 runs some newer stuff. Most of the recent programs that still support PPC require 10.5
And MorphOS is to fulfill your Amiga needs

@ haywirepc
You may like
this AmigaOS 3.x skin if you're finding MorphOS's visuals not to your liking. I use this one and am quite fond of it!