Today Gutsy automatic update brought in a new kernel and required a reboot. The reboot failed with a scary message after the grub prompt. After a few moments of panic, I remembered the command prompt available from grub and typed
This told me that it found them on hd1,0, hd1,1, and hd3,1. Looking at the script the update had inserted I saw that it was referencing hd0,0. Changing that to hd1,0 using the built-in editor allowed the boot to proceed. Once I had the machine up I edited /boot/grub/menu.lst to fix that error.