It's gone? do you mean you formated the partition?
Otherwise editing the file /boot/grub/menu.1st and adding this should do the trick.
CODE
title Windows XP
[TAB]root (hd0,0)
[TAB]makeactive
[TAB]chainloader +1
(where it says [TAB] it indicates that you should indent with a TAB)
and BTW you can ofcourse use any title I just assumed it was Windows XP you had on the drive
/LinuxSam