I took some logos of different Linux distributions, other operating systems or desktop environments, worked on them a little with GIMP and saved them. The icons are 128x128 big and in PNG format.
The goal of these icons is that you can use them on your desktop for an emulator.
(I don't know if Mac OS is running in QEmu, but the icons are there ;-).
Please let me know if you have some additions. IMHO the Gnome, Apple and Knoppix icons are not that good, but I didn't get it any better.
Have fun! :-D