Which installation guide did you use?
Newer Macbooks are using UEFI, actually a specific type of UEFI. Linux Mint 13 (like many other Linux distros) are using grub2 as bootloader, and there are still some issues with grub2 (release 1.99).
Since you are able to get to the grub menu, it looks like the UEFI boot is working. I would boot the live DVD and check the following on your hard drive:
1. grub.conf file in /boot/grub - you need to mount your hard drive first. See if the menu entries are correct and point to the right kernel files.
2. The /boot folder to see that the kernel files are there.
3. Check that the live DVD is OK (mdm5 check).
Unfortunately I'm traveling and only have my Macbook with me so I can't check other options.
Here are some links that might help:http://www.rodsbooks.com/refind/http://forums.linuxmint.com/viewtopic.php?f=46&t=103048http://johnatilano.com/dual-boot-mac-os-x-and-linux-mint-9-on-a-macb
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