When you install Windows on your Linux box, GRUB (GRand Unified Bootloader) is washed away from the MBR, because windows writes its own bootloader to MBR. (Here I assume that no windows was installed before Linux installation). If you are successful to write GRUB to MBR (how?), it does not contain the entry for your new Operating System (Windows). Now you need to edit the GRUB configuration file. And if you are a newbie to Linux, you don't know what commands to write in order to create the entry for Windows. For Ubuntu users, I've found an easy method to do that, and it requires no command.
