I've got last week an iMac G5 12.1, too, and it works very good with Morphos 3.13, except of course the missing boot-picture. But a much bigger issue is the not working Wifi. If the Wifi is turned on during installation, the computer will freeze after short time, if I open a window I will get the message "Application is meditating". With Wifi switched off during installation and Internet through good old LAN there is no problem at all.