Ubuntu 9.10 Karmic Koala uses GRUB 2 rather than GRUB. People with dual boot systems may find their Windows installation missing from the GRUB menu after installing Ubuntu 9.10.
Do not bother with editing the /boot/grub/menu.lst file as this is GRUB2 we're dealing with now.
To add or restore your Windows installation to the GRUB 2 menu, simply issue the following command in a terminal window:
Related: Restore an Overwritten GRUB Boot Loader