Here's how I reinstalled grub on my Ubuntu installs:
grub> find /grub/stage1
(hd0,0)
grub> root (hd0,0)
grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... no
Checking if "/grub/stage1" exists... yes
Checking if "/grub/stage2" exists... yes
Checking if "/grub/e2fs_stage1_5" exists... yes
Running "embed /grub/e2fs_stage1_5 (hd0)"... 17 sectors are embedded.
succeeded
Running "install /grub/stage1 (hd0) (hd0)1+17 p (hd0,0)/grub/stage2 /grub/menu.lst"... succeeded
Done..
Additional Information
"error 15: file not found" on startup
Ubuntu how to re-install grub using chroot