How to create a triple boot system (MacOS, Ubuntu, Windows) on a MacBook.
Note: This was created using a 2008 MacBook running Max OS X 10.5.4.
Under construction
This page is under construction!
Disclaimer
Things are a little bit tricky with a Mac. You can obviously mess up your system if something goes wrong. So: Please backup your data before you start and read the instructions carefully.
This page intentionally explains one way in a (hopefully) simple and step by step manner.
Summary
In short, here's what you do:
Update your MacBook firmware to the latest available version.
Install rEFIt.
- Create partitions for the three operating systems.
- Install Windows and Ubuntu Linux.
Step by Step
Update your MacBook's Firmware
This is just to make sure that you're running the latest available firmware. Firmware updates are distributed as part of OS X updates, so this part is pretty easy: Boot into OS X, make sure you've got a working Internet connection and click on the Apple-Symbol in the top left corner. Select "Software Update" and install the updates.
Install rEFIt
If all goes well, you're going to have three operating systems to chose from at the end of the day, so you'll want to be able to chose which OS to boot into upon startup. You will also want to keep your partition tables in sync. rEFIt does both of these things for you.
In case you've never heard of "keeping partition tables in sync", just note that so called "GPT/MBR hybrid" partition table is needed to make all three operating systems happy. See the rEFIt website (http://refit.sourceforge.net/) for more information, and make sure you understand the importance of syncing your partition tables.
To keep things simple: Download the Mac-Disk-Image from the rEFIt site and use it to install rEFIt to your harddrive. Once the installation is finished, you can reboot and enjoy the pretty REFIt menu. 
Create partitions for all three operating systems
Instead of using Apple's graphical "Disk Utility", we'll go for the good old command line, so open a Terminal and have a look at your existing disk layout:
diskutil list
So we've got 2 partitions here already (disk0s1 and disk0s2 in the example). The first one is the so called EFI partition and the second one is the Mac OS partition. Leave the EFI partition alone and split up the Mac OS partition in three:
diskutil resizeVolume disk0s2 45G HFS "4-Linux" 20G MS-DOS "4-Windows" 0b
So now we've got 4 partitions. In the example partition 2 (Mac OS) was shrunk to ~ 45 GB, partition 3 (labeled "4-Linux") was made ~ 20 GB and partition 4 (labeled "4-Windows") uses the rest of the space on the harddisk (approximately 84 GB).
Remember that this was done on Mac OS 10.5.4. I don't know if "diskutil" works the same way in previous versions of Mac OS (especially the non-destructive resizing of partitions). If anyone gives it a go, please comment here. You may want to have a quick look at the manual page of diskutil just to make sure, you know what you're doing.
man diskutil
Note that your Windows partition will need to be the last one. Otherwise you will probably get strange errors halfway through your Windows installation (at least with Windows XP).