Please boot into Ubuntu (with the LiveCD) and post
sudo gparted /dev/sda
[COLOR="Red"](This is not a malicious command!! Normally you should never execute commands like sudo something or sudo gparted ..., but see the man page for gparted, see also Announcement about malicious commands)[/COLOR]
For my MacBook it looks like:
/dev/sda1 200MB EFI /dev/sda2 hfs+ 65GB /dev/sda3 Swap 1G /dev/sda4 ext2 75gB
How large is your hard drive, that you have that much disk space? And you need only twice the RAM size for swap space.
You want a dual boot system, right?
You need to install grub into your root partition. You need to sync the GPT with the partition table, using for example rEFIt. And, if you don't want to press the Alt-Key every time you boot, you need a boot manager like rEFIt. See the Mactel start page, it features a link to a generic install instructions.
You tell during the last install step, to install grub to the MBR of the root partition. You can also install grub after the install, but that is also quite dangerous. come back here if you want to know how that works.
Unfortunately, there is no wiki for the MB2-1 for Intrepid. You might try the wiki for MB3-1/Intrepid. If you like to, note things that differ from the wiki for the MB3-1!