Why won't my MacBook Pro boot from a Linux Live CD?
Macs use the EFI Firmware (BIOS for Windows).

You need to download a special Mac ISO that allows to boot on both BIOS and EFI Systems.


For Ubuntu 11.10 you can download the specific Mac image here:
64-bit Mac (AMD64) desktop CD

By experience I know that the following distros allow to boot on EFI systems using the "standard" ISO: Debian, Fedora, Linux Mint


Your questions is related to this here on askubuntu.