How do I choose to boot Ubuntu on PowerPC

[emailkia]

I am new user of PowerPC with a G4 machine. I am also completely new to Ubuntu. Just for hours ago I managed to install Ubuntu 6.06 on the PowerPC. First time I rebooted so automatically Ubuntu booted and I could use it. Second time MAC booted and I didn't have any choice to boot from Ubuntu. Now I have Ubuntu but I don't know how to boot Ubuntu when I am starting my MAC. What should I do?
Thanks

[linear]

Did you use Startup Disk to switch back to OS X? If so, instructions to fix booting are here (https://help.ubuntu.com/community/YabootConfigurationForMacintoshPowerPCsDualBoot). (Look for the section titled "You lost the yaboot menu! Now what?")

[Auria]

You can also probably just hold down 'alt' during startup