This is what I followed to install ubuntu as a dual system for my mac air.
I have finished installing ubuntu in my mac and I can see the icon in the interface of rEFIt.
But when I selected it and typed enter, I just got a black screen.
As this article said, I need to install GPT fdisk and build a hybrid boot menu.
So I install the GPT fdisk in the OS X. but for the hybrid boot menu, I really don't understand how to build it even if there is another post: http://ubuntuforums.org/showthread.php?t=1810275&page=19&p=11215214#post11215214
Can any one help me to build a hybird boot menu?