I found a way to bypass the grub problem on my macbook (I use only linux no refit or bootcamp)
Install Mint 4.0
Boot with the LiveCD
open a shell
sudo mkdir /mnt/mint
sudo mount /dev/sda1 # maybe different on your system
sudo mount -t proc none /mnt/mint/proc
sudo mount -o bind /dev /mnt/mint/dev
sudo chroot /mnt/gentoo /bin/bash
sudo apt-get install grub
yes
sudo nano /boot/grub/menu.lst
comment gfxmenu line
comment color cyan line
remove quiet splash from kernel /vmlinuz-2.6.22-14-generic root=/dev/hdc3 ro quiet splash
then sudo grub-install --no-floppy /dev/sda1
exit
sudo umount /mnt/mint/dev
sudo umount /mnt/mint/proc
sudo umount /mnt/mint
sudo reboot
should be ok now



