Ok, so here's my menu.lst file - see anything that jumps out?
title Ubuntu, kernel 2.6.17-10-generic
root (hd0,1)
kernel /boot/vmlinuz-2.6.17-10-generic root=/dev/hda2 ro quiet splash
initrd /boot/initrd.img-2.6.17-10-generic
quiet
initrd /boot/initrd.img-2.6.17-10-generic
quiet
savedefault
boot
title Ubuntu, kernel 2.6.17-10-generic (recovery mode)
root (hd0,1)
kernel /boot/vmlinuz-2.6.17-10-generic root=/dev/hda2 ro single
initrd /boot/initrd.img-2.6.17-10-generic
boot
title Ubuntu, memtest86+
root (hd0,1)
kernel /boot/memtest86+.bin
quiet
boot
### END DEBIAN AUTOMAGIC KERNELS LIST
# This is a divider, added to separate the menu items below from the Debian
# ones.
title Other operating systems:
root
# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/hda1
title Microsoft Windows XP Professional
root (hd0,0)
savedefault
makeactive
chainloader +1