I have the same problem with the new Grub2 and I can't triplee boot WinXP,Ubuntu and Zephyroth's Mac 10.5.2 Rev2 for AMD.The grub2 added the Mac's menuentry but when I try to boot it it gives me just kernel panics whatever I try to do.I tried to edit the grub.cfg file in every possible way but with no any success.But when I restore the EFI in MBR I can boot very well in WinXP and Mac,but no Ubuntu then(even with Grub2 installed in its own partition).I guess the only way is to downgrade to the grub legacy in Ubuntu and to chainload the Mac's entry manually in the boot/grub/menu.lst,like in the old fashion way.