add the option manually into the /boot/grub/menu.lst as below:
press ALT+F2 to get a run dialog.
enter below lines and press enter to get gedit opens the file for you.
Code:
gksudo gedit /boot/grub/menu.lst
when prompted give ur password.
enter below lines to the end of the file and save exit.
Code:
title Microsoft Windows 98 SE
root (hd0,0)
savedefault
makeactive
chainloader +1
I hope ur windows os is installed on ur first harddisk's first primary partition.try reboot to get the entry in GRUB.if u cant boot into windows again.post ur "sudo fdisk -l" output from a terminal.
btwn post in Open Source section for better responses atleast next time.