Triple Boot (OSX - Windows XP - Ubuntu Linux 8.04) on the new MacBook (Late 2008) UPDATE: Works for 10.04

I had some issues finding a guide for exactly what I wanted to do, so I adapted my own:

Major Steps:
1. Partition Hard Drive
2. Install rEFIt
3. Install Windows
4. Install Ubuntu


Partition Hard Drive
(Do not use Boot Camp to partition, it will give you trouble)

• In OSX open up Disk Utility (Finder > Applications > Utilities)
• Click on your hard drive and click "Partition"
  
• Click the "+" and create two new Partitions.
• Name and size them as you see appropriate. Format the Windows partition as FAT32. Size them as you see fit. I gave "Ubuntu" 10GB and "Windows" 40GB.

Install rEFIt

• Download rEFIt: http://refit.sourceforge.net/doc/c1s1_install.html
• Install rEFIt: http://refit.sourceforge.net/doc/c1s1_install.html
• If rEFIt did not show up on reboot after the automatic install try the manual install.
  

Install Windows

• Insert your Windows CD
• Reboot
• Hold down "C" during start-up to boot to the Windows CD
• Install Windows to "C:" (Which should be the drive you created)
• Install the drivers windows drives from your OSX CD.

Install Ubuntu (This process has been tested on 8.04 and 10.04)

• Insert your Ubuntu CD
• Reboot
• Hold down "C" during start-up to boot to the Ubuntu CD
• Select Install Ubuntu
• Manually Partition the Hard drive when asked. Select sda3 and set it as /.
• IMPORTANT: on the last step of setup click advanced and install grub onto sda3.
• Let Ubuntu Install
• Reboot
  
• Sync the partition table in rEFIt.

You should be good to go!

Sources:
http://wiki.onmac.net/index.php/Triple_Boot_via_BootCamp
http://blog.gnist.org/article.php?story=Triple-Boot-OSX-Ubuntu-Vista