Boot into rhe and use update-grub.

OR

I don't use the chainloader but rather specify which partition and kernel I want to boot in /boot/grub/menu.lst like so:

Code:
title             Debian
root            (hd0,1)
kernel        /boot/vmlinuz-2.6.8.1 root=/dev/hda2 ro 
savedefault
boot
HTH