Macintosh PowerBooks these days come with a CD/DVD drive but not a floppy drive, but the Linux distributions for PPC support booting and installation off of a CD without any need for a floppy.
Sometimes, when you boot the installer on the PowerBooks, the screen is black; this is easily fixed by tapping the brightness key on the keyboard (somehow, the screen brightness gets reset to zero).
If you have a very recent PowerBook, it may not be supported by the kernel on the installation CD. You can get around this by booting off of a recent kernel downloaded onto your hard drive and using a ramdisk on the CD or hard drive, while still loading the installation packages from the CD (the default). (See the instructions available online for yaBoot or BootX, the Linux/PPC boot loaders; yaBoot is currently better-supported on the newest machines.)
They can also boot/install from the Macintosh (HFS) partition on the internal hard disk.
This part is a courtesy of Steven G. Johnson.
See also iX issue 1/2000 of the German computer magazine p. 74: Aepfel auf Reisen by Anna Kobylinska and Filipe Martins (LinuxPPC 1999 Q3 and Yellow Dog Linux 1.1).