ElDiabloConCaca
U.S.D.A. Prime
Linux requires a minimum of two (maybe three?) partitions in order to run. It required a boot partition, a home partition, and maybe some others. You need to partition your hard drive into one OS X partition, and one UNFORMATTED (free space) partition. To do this with Disk Utility, select the disk (not the volume) that you want to partition, and select "Two partitions" from the drop-down menu in the "Partition" tab. Choose "Mac OS X Extended (Journaled)" for one partition (for OS X), and "Free space" for the other partition.
Then, boot back up from the Linux CD, and choose the auto-partition method for the free space partition. The boot partition should be relatively small, while the user or home partition and other partitions should be a lot larger, since those partitions are where Linux actually installs to.
That "free space" partition may or may not need to be the first partition on the drive -- check the install instructions online (I don't believe it has to be, but I could be wrong). That should get you up and running with a dual-boot OS X/Linux install!
Then, boot back up from the Linux CD, and choose the auto-partition method for the free space partition. The boot partition should be relatively small, while the user or home partition and other partitions should be a lot larger, since those partitions are where Linux actually installs to.
That "free space" partition may or may not need to be the first partition on the drive -- check the install instructions online (I don't believe it has to be, but I could be wrong). That should get you up and running with a dual-boot OS X/Linux install!