iMac + Ubuntu: How-To?

Hey everyone. I'd like to give Ubuntu a shot on the iMac. I've used Ubuntu before on the X86 platform. My trouble comes from not knowing the intricacies of slipping it into the computer properly. When I boot off the Ubuntu desktop or Ubuntu alternate CD, I just get a blank colored screen after entering the boot argument, and this happens no matter what argument I tried.

Yes, both discs were PPC. I checked. Just wondering if anyone else has experience with this. I was trying to install Lucid Lynx (10.04).

Thanks for any help!