Normally grub reads its menu.list (or in some cases grub.conf) from the /boot/grub directory and displays a graphical list of boot options. Assuming that for some reason it cannot display these, it will default to a command line boot-loader.
If I recall, you must tell it the boot partition on which it will find the kernel (partition 1 is 0, 2 = 1, 3=2 and so on) with the command "root (hd0,0)" - if your boot partition is disk 1, partition 1. Then you must tell it what kernel it is to boot with "kernel /path/to/kernel" - as it says, you can use TAB completion to help you find the name, it will probably be something like kernel /boot/vmlinuz-2.6.27.img or such.
Then you need to pass it the options of what root filesystem it will be mounting after it has loaded the kernel (assuming that the boot partition and main partition are separate) this is done by providing the kernel with the root=/dev/hda2 parameter on the command line (again, assuming that your root partition is /dev/hda2).
My grub knowledge is somewhat hazy, googling about grub booting would probably yield far more useful information.