How to Install Grub On Ubuntu

1, Boot into your ubuntu

2. go to the terminal

 ( you just need to update you grub so that it can find the windows 
 installation, this can be done by the following command )

#:~$ *sudo update-grub2*
 [sudo] password for ubuntu:
 Generating grub.cfg ...
 Found Debian background: apollo.tga
 Found linux image: /boot/vmlinuz-2.6.31-15-generic
 Found initrd image: /boot/initrd.img-2.6.31-15-generic
 Found linux image: /boot/vmlinuz-2.6.31-14-generic
 Found initrd image: /boot/initrd.img-2.6.31-14-generic
 Found memtest86+ image: /boot/memtest86+.bin
 Found Windows xp (loader) on /dev/sda1
 done

 3. try reboot again , now you will see windows xp in grub menu