When I first got my Macbook Pro, I was not exactly computer savvy, but in the spirit of forwarding that goal I decided that I needed my computer to have a Mac, Windows, and Linux OS. And I wanted native booting, not virtual machines. The process of triple booting on a Mac is not that hard if you know what you are doing, but as I had no idea what I was doing, it took me a while to figure out. I cobbled together numerous tutorials and help pages and I am posting my version here so that others might make use of it.
This isn't exactly something I built, but I think it is in the spirit of 'Building Stuff, Makin' Friends' (though I guess I pretty much decide the spirit of this place anyway). So, without further ado, the tutorial.
A summary first:
This tutorial assumes you have a Mac, with the Mac OS already installed. It also assumes no prior partitions on your drive. Furthermore, it assumes that your Windows install CD is exactly that--a SINGLE install CD (you won't be able to eject during the install process because you don't have the drivers for that installed!).
What you will essentially do is this: Install the rEFIt boot Menu, use Mac to make your partitions, install Windows first, install Linux second. The rest is just details.
What you need:
Mac install CDs (I have Leopard)
Windows install CD (I have XP)
Ubuntu (I used 8.10, the 64-bit version. The download is free. Burn it to CD with Disk Utility)
Download and install rEFIt.
Use the terminal (Applications->Utilities->Terminal) to write partitions. This assumes no previous partitions. (Type the stuff in italics. Be warned! This stuff can be dangerous. If you are not sure of what you're doing, back up your data, and maybe read up on these commands before executing them.)
sudo diskutil resizeVolume disk0s2 249G "HFS+" "Linux" 17G "MS-DOS FAT32" "Windows" 32G
Disk0s2 should be the Mac volume. I wanted to leave 249 GB to it, and put 17GB aside for Linux and 32 for Windows. The three sizes must add up to less than your total available space on the drive. The command diskutil list will show you the partitions you have set up.
Windows will have to reformat the partition it will be using, otherwise it will install but not boot. I did this to get the installer to give me that option:
sudo dd if=/dev/zero of=/dev/rdisk0s4 bs=1m count=100
That writes over the metadata for that partition, making it Unknown Format to the installer. Alternatively, it seems like you can also just delete and recreate the partition in the Windows Installer instead of using the partition you created with the Mac OS. I prefer the former, though, because I know it worked for me.
Install Windows by putting in the CD and restarting with key C held. After setup, choose the right partition to install to. It will restart a few times, so make sure to boot into Windows to complete the process. After it is done, use the Mac OS install CD to install the drivers for Windows (for older Macbooks it may be necessary to find these drivers in BootCamp and burn them to a CD).
Next, put in the Ubuntu CD and boot it as a live CD. Open up the terminal. Back up the MBR (Master Boot Record). I don't remember if you need to use sudo to get this to work. If permissions are denied, just add it in.
dd if=/dev/sda of=/tmp/sda.mbr bs=512 count=1
Run the installer (it is sitting on the desktop). Choose to partition manually. Select the right partition (sda3 should be it) and press Edit partition. Choose to mount to '/', to format it, and to use ext3. Go to next and ignore the error message about swap. When offered the install summary, look at the advanced options (important!). Install the boot loader on sda3 (your Linux partition) and not on the default (that will make Windows unbootable and none of the fixes I found actually worked without jeopardizing the rest of my systems).
Restore the mbr. I'm not sure exactly when this is supposed to be done but I did it after hitting install and it worked fine. Again, in the terminal:
dd if=/tmp/sda.mbr of=/dev/sda
Wait for the installer to finish. Restart as necessary. Actually, try to shut down instead of restart, because at this point there's a bug that I experienced where restarting freezes my computer on the restart part. Shuts down works fine though, so shut down and press the power button.
Update the MBR by using the Partitioning Tool in rEFIt. When prompted, choose Yes to update. Boot Linux. I had to try booting it twice, but that seems to just be a fluke. I had a lot of those during this process, actually. Make sure all problems are real problems by checking if they happen at least twice.
Finally in Linux open the terminal to make a swap space. Use sudo when permissions are denied.
dd if=/dev/zero of=/swap bs=1024 count=1048576
chmod 600 /swap
Now check all your systems to see if they boot properly.
An afterword: who needs that many operating systems anyway?
Well, I do. Since installing all three operating systems, I have found that I use them pretty equally. I use Linux for certain robotics and programming projects, Windows for gaming and other programming projects, and Mac just because it works best with this particular machine and also for programming certain things, like Widgets. There are a lot of things I wouldn't have tried if I didn't have the right OS, but now I can run just about anything. And now that I created a 32-bit environment in my Ubuntu for compiling 32-bit code, I can really run just about anything.
Hope this helps you out!