I ran into this tricky problem that I thought I better share with you.
I have an Ubuntu (7.10) machine on which I wanted to install OpenSuse 11.0 in dual boot. I thought I could simply add Suse to my existing (Ubuntu) grub-menu. However after installing Suse (I skipped the grub install that suse proposed), adding suse to my grub-menu and booting, grub would fail when I tried to boot Suse. Errors were 'Error 2 : Bad file or directory type' or 'Error 15 : File not found'.
As it worked out Suse had formatted the root-partition with an inode size of 256 (the new default for the ext3 filesystem) but the (legacy) grub can not read this format. :-( See a good explaination of this problem here: http://www.linuxplanet.com/linuxplan...orials/6480/1/
You could try to solve this by installing a newer grub or use the grub that suse 11 comes with but I choose to reinstall Suse and tell the partinioner to format with inode-size=128 (hidden in the expert options)
I really think that the Suse install manual should warn you for this but it does not.
Hope this helps one or two of you.