triple boot on mac with ubuntu

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https://bbs.archlinux.org – i have a macbook pro 5,5 if that helps, i installed ubuntu on the macbook with refit and i now want to install arch  as well. i discovered that i can not see any partitions after four on my mac and therefore can not have a boot partition for arch and ubuntu has the grub boot on its partition, my questions are should i and how do i add arch to ubuntu's grub and boot from there, or is there a better way that gets around the four partition problem.i apologize if this has been asked before but my searches came up with nothing thanks xcabal https://bbs.archlinux.org/profile.php?i (HowTos)