After upgrading to squeeze the new grub was chainloading through the old one. It was working fine, so I elected to run upgrade-from-grub-legacy. After this grub was failing with "Error 15", not even giving me the option to press a key to restart. I can boot now using Super Grub Disk. I want to revert back to lenny's grub, and not use the new grub from now on. How can I do this?