To find the root partition,@ the grub prompt
grub> find /boot/grub/stage1
grub> find /grub/stage1
It will return something like hd(0,8)
grub> root (hd0,8)
grub> setup (hd0,8)
The above 2 cmds have been discussed in the previous posts,Just giving them for the sake of completion.
BTW,u will be getting the grub prompt by just typing typing 'grub' @ the command prompt