Booting 64-bit Linux on a Macbook5,2

[Patrick Doyle]

Help,
I don't know where to turn here.  It seems that every thread I've
found that describes this ends with "and now it works", but I can't
seem to get there.

I have installed 64-bit Ubuntu 10.04 on a Macbook5,2.  I would like to
boot this without the acpi=off parameter that is currently required.
Once, in the past, I installed grub-efi in the /efi folder and was
able to boot a 32-bit Ubuntu installation on this hardware.  But I
have since installed the 64-bit version and can no longer get it to
boot.  It gets as far as displaying the message about loading initrd
and stops there.

Can anybody help me figure out where to go from here?

--wpd