Which ubuntu version are you trying?
The white screen with black text is normal. It shows video hardware detection details.
For different boot-options look here PowerPCKnownIssues.
If you only want to install, I suggest to take the alternate cd. It comes with a non gui installer.
On my ibook G4 the standard ppc hardy live CD is working fine in default boot (type nothing on the first boot screen).
And there comes up two times this error message:
But then startup will continue.
Cannot allocate resource region 0 of device xxxxxxxx