It's alt+opt(apple or windows logo)+o+f for the openfirmware prompt.
setenv boot-device <CD/DVD drive><0,1,2, the one in order>
You have the wrong CDs.
Debian and fedora have active PowerPC support.
You can try Yellowdog.
All of the BSDs have PowerPC support. OpenBSD is probably the easiest.
Partitioning is done differently. You will need an Apple boot record, a hfs/hfs+(NewWorldBoot), a swap, and a master partition. There isn't a limit on partitions as there is with DOS MBR tables.
There are Howto's for installing on the Debian and FreeBSD forums.
OpenBSD install applies to all architectures, unless otherwise noted.