Create windows entery in grub boot loader

first of all you need to execute one command in the terminal and that is this...

$ sudo gedit /boot/grub/menu.lst
the text file is open and this have information about boot loader

you can write these in file

title Windows XP
root (hd0,1)
makeactive
chainloader +1

after this save the file and close .
you can boot in either linux or windows

REINSTALLING GRUB

>> boot from the linux's LIVE cd without making any changes to your system and any of your partitions.

>> open up the terminal AND TYPE COMMAND
sudo fdisk -l

and check the linux system in it
if linux is there then type next command

$ sudo grub
-find /boot/grub/stage1
(hdx,y)

- root (hdx,y)
- setup (hdx)
- quit
- exit

thats all you need to and you will get you linux back and your window will be there too....