[other] How to add Windows 7 in GRUB bootloader

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http://ubuntuforums.org – I dont have windows 7 in my grub bootloader..and i selected UBUNTU as my default OS.Now i cant boot Windows 7.:mad::mad: Pls tell me how to add windows 7 in grub menu. I also tried to changing the 40_custom file but it is read only so i cant change. Help I am using UBUNTU 12.04 LTS (Hardware)