Here's a quick guide from what I've done:
Things you'll need:
1) Ubuntu LIVE CD
1) Boot the Ubuntu LIVE CD by restarting your computer (enter your BIOS menu and change your #1 boot priority as Cd/Dvd).
2) Insert the Ubuntu LIVE CD.
3) Choose a language and select the first option.
4) Go to terminal and type sudo -i (this command is to change the current account as root. From now on you don't need to type sudo for every command you want to use)
5) Type grub
6) Find where is your boot folder (which stored your GRUB) by typing find /boot/grub/stage1. Remember the location (it should be something like (hd0,2). I'll be using(hd0,2) as example for the steps below.
7) Type root (hd0,2)
8) Type setup (hd0)
9) Exit grub by typing quit.
10) Reboot your computer by typing reboot.
11) Eject the Ubuntu LIVE CD and the menu should be restored (only if it worked last time before the windows bootloader overwrite it)
* The first partition will always enumerated with 0. In the example (hd0, 2). The number 0 means it is the first physical hard disk and the number 2 represents the partition where GRUB is installed.