ACPI is n/a for ppc. Same for apm. Those don't work with the ppc hardware. Pbbuttonsd controls sleep and hibernate. And for PPC Linux, you must have an ATI graphics card for sleep to work. Nvidia and anything else will not work.
$ sudo pbbcmd hibernate
or
$ sudo pbbcmd sleep
or
$ sudo pbbuttonsd sleep
or
$ sudo pbbuttonsd hibernate
