I am installing ubuntu on my MacBook, following the instructions here:

http://www.rodsbooks.com/ubuntu-efi/index.html

Everything has gone well so far. But I have now come to number 19. The cd with GRUB2 is in the drive, but when I type 'sudo apt-get install grub-efi' it says:

package grub-efi is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it: grub2-common grub-common

The Grub iso I downloaded and burned was this one:

http://forja.cenatic.es/frs/download.php/1381/super_grub_disk_hybrid-1.98s1.iso