had trouble trying to revert Ubuntu 10.04 LTS from grub2, won't boot mdraid and did not even install mdadm during the installation!
I have tried moving back to GRUB 0.97

backed up original /boot and then copied /boot from an old Debian install.  Modified device.map and menu.lst and put the appropriate kernels and initrd for Ubuntu back in /boot

I ran grub:
root (hd0,1)
grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  16 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+16 p (hd0,1)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded
Done.




I was successful.
But when booting I get a _ line that goes from top to the bottom and ends with a weird face/shape inside a rectangle.
I even wiped out the MBR dd if=/dev/zero of=/dev/sda bs=512 count=1 and then ran grub setup again as above with the same result.

I believe the issue is in the boot sector of /dev/sda2 where grub is, perhaps grub2 installs something/in addition sectors that grub 0.97 cannot erase or overwrite.