For some time i had ubuntu installed on my ibook (just to check it out). In my experience it's extremely difficult to repartition the disc for linux, without messing up the osx partition. I did a fresh install to make it work. (My linux abilities are near zero, i followed a guide to install it. There might be some easy way to repartition the hd, without destroying osx.)

I installed a bootloader so that i could press either "x" or "l" depending on what i wanted to boot into.

As far as i recall you could press "alt" too, and choose it among the other partitions just like any other osx install...
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- iMac g5 2ghz, 1.5gb ram.
- eMac 1ghz (clocked at 1.27): 1gb RAM, Dual Layer Pioneer DVD +/- RW, 80 gb HD, 160 & 250 external Lacie FW HDs. And modified cooling.
- iMac 600 mhz
- b&w in atx case, with sata drives :p
- PowerMac g3 b/w - with atx psu
- PowerBook G3 Wallstreet