I have been trying to do that for a while now, but in the end, Moblin and grub where not very good friends… until now! Moblin 2.1 and Ubuntu Karmic Koala (or maybe I should say grub2) have decided to put their differences appart and coexist.
To make this possible, download the latest version of Moblin from their web (Moblin 2.1 right now) and install it. In the last step, UNCLICK the option where it says install loader to blablabla. We will handle Moblin trough grub2 in Ubuntu. Once you are done, reboot and login in Ubuntu. Open a terminal an type sudo update-grub. This time, grub will detect an “unknown linux distribution” and it will make an entry available in the menu when you boot. Don’t believe me? Go ahead, restart the computer and select that suspicious “unknown linux distribution”…
Voila! Welcome to Moblin! I’m writing this post from it, so this is the proof that it works. It runs pretty smoothly and has some cool changes (like Mozilla-based browser, for example).

Now I have grub configured on my Samsung NC10 to boot either Windows 7, Jolicloud, Ubuntu 9.10 or Moblin 2.1. Yay for diversity! Somebody said something about Chrome OS? :)