by Forrest Sheng Bao http://fsbao.net
I just got a new iMac. Yes, the latest Apple iMac, the 24-inch one, with 4G DDR3 memory, 2.66GHz Intel Core 2 Duo CPU (almost 15, 000 integer MIPS (Dhrystone) and 5,000 floating point MIPS (Whetstone)), and nVidia GeForce 9400M graphic processor.
Ok, so, how to install Ubuntu on an Intel-based iMac? There is a good instruction for you at Ubuntu Help. https://help.ubuntu.com/community/MactelSupportTeam/AppleIntelInstallation
The general idea is:
1. Google, download and install rEFlt. Make sure that you can see its interface when you boot up your Mac. Most likely, you need to SHUTDOWN the Mac and then start it. RESTART does not work. If you update your Mac OS X, Mac OS X may rewrite the bootload. So you need to reinstall rEFlt in Mac OS X. It should be look like the one on rEFlt official website, but without Linux and Windows option, just a Mac OS X.
2. Prepare the partition for Linux. You can use BootCamp Assistant or Disk Utility to do so. I splitted a big partition for Linux and used Ubuntu installation program later to do further partitioning, i.e. one for / and one for swap.
3. Insert Ubuntu installation CD into Mac and reboot your Mac from it. Install it. Do remember to install bootloader on the Linux root partition (NOT MBR or other places) by clicking Advanced button like this:
This is how my bootloader selection menu looks like.
Update 2011-12-23: I fully swiped out Mac OS X on my iMac. Now it has only Ubuntu Linux. This is how the bootloader selection look like now.
4. Reboot when done with the install, and in the rEFIt menu, choose the partition tool. It will attempt to sync the partition tables on your disk. Then SHUTDOWN the computer (not reboot), and start it up. You should be able to boot to Ubuntu now.
Here is a video regarding how Linux booted from my iMac.