Here is how I did a triple boot machine, after trying all the other methods on the site. I went with Win7RC, Ubuntu, and OSX. I gave up on the GUID partition map and went with the old standby MBR partitioning, and that was the key to getting it all working. I was fortunate enough for Dell to send me a 64GB SSD
for a warranty replacement of my 32GB SSD
when it died, thus giving me even more desire for a triple-boot unit.
NOTE: This guide is in a very rough form but I will edit it to fill in details. It appears several of you are trying to do the same as me, so I thought rough was better than waiting. Maybe this will become Sticky material in a few days.
For prep work, I have several USB keys created. For some of them you could use installation CD/DVD media.
4GB Key #1: Windows 7 built using the thread Win7 on USB in 4 easy steps. This could be the DVD instead.
1GB Key #2: Ubuntu Netbook Remix 9.04. You could just use the CD.
8GB Key #3: MacOS 10.5.0 modified for MBR install and built using the fine instructions in the DellEFI Guide v3 thread by mechdrew. There is a thread that tells how to edit the OSInstall.mpkg to allow for MBR installations.
I partitioned my 64GB drive using diskpart on the Win7 media. I did them in this order, using an MBR partition format (if you use OSX DiskUtility):
Partition 1: 24GB FAT32 for my Windows 7
Partition 2: 24GB FAT32 for my OSX
Partition 3: 8GB FAT32 for my Ubuntu
Operating System #1: Windows 7
Boot the Win7 key and install Windows 7 to the first partition. You have to format the partition in the setup so it becomes NTFS. I see no reason why this couldn't be XP.
Operating System #2: Ubuntu
Boot the Ubuntu key and install Ubuntu. Pick manual partitioning and select the 3rd partition for use, formatted as ext3 and mount point is "/". In step 7 of the install, select the Advanced tab and install the boot loader to /dev/sda3.
Operating System #3: OSX
Use the DellEFI Guide v3 to install the operating system. It's an excellent guide!
When you are done, you be using the Mac Chameleon has your boot loader. If it gets wiped out, it is easy to reinstall by booting from the OSX install USB and getting back into OSX to re-run DellEFI.
Hope this helps get you going! You could easily skip one of the two operating system to get a dual boot OSX system with Win7, XP, or Ubuntu.