I managed to install 10.04 on a system that already has 8.04 (separate partitions, of course). It also installed GRUB2 onto the MBR.

After discovering that there is no menu.lst anymore, I edited /etc/grub.d/40_custom to point to where my other OS partitions are:

menuentry "Ubuntu 8.04" {
set root=(hd0,0)
linux /boot/vmlinuz-2.6.24-28-generic
initrd /boot/initrd.img-2.6.24-28-generic
}

menuentry "Windows 7 Ultimate 64-bit" {
set root=(hd0,2)
chainloader (hd0,2)+1
}

GRUB2 displays the menu with those entries but when I select any of them, it refuses to load them, saying "No such partition".

I know the partitions are there, as 10.04's "Disk Utility" sees them without any problem.

How do I get GRUB2 to recognize them?