Today I installed a second operating system to my laptop and I was surprised that Ubuntu did not automatically add the new operating system to GRUB. The solution is simple. To add another operating system to grub type the following into the terminal:
gksudo gedit /boot/grub/menu.lst
Scroll all the way to the bottom of the file and type the following:
title Your New Operating System’s Name
Let me explain a bit about this command. The root (hd0,0) command will probably have to be changed in your case. “hd0″ is related to the hard disk. If you only have one hard drive (like most people) leave this alone. Now the second part after the comma is related to the actual partition. My new operating system is located at hdc3 so I changed the command to root (hd0,2). Whatever partition your new operating system is located at, you will need to change this number to be one less. For example: hdc1 becomes root (hd0,0), hdc2 becomes root (hd0,1), hdc3 becomes root (hd0,20), etc. You get the point.
Resave the file and reboot and you should be able to boot into your new OS.