Dual Boot

Sure, use the System Disk control panel that's installed with the OS. Or hold down option when you start up.
I wouldn't recommend yaboot for anything other than Linux. It's mostly designed around the goal of booting non-Apple operating systems. OS X's System Disk panel does a decent job.
You could boot to the OBP (Open Boot Prom) by holding down CMD-OPTION-O-B (i think).

Then use setenv auto-boot? false to stop the OS from booting, set two device aliases, then when you boot you go to a prompt and can type:

boot classic
boot x
or boot cdrom

This said, the option key is a far nicer option!