Type ? to see a list of commands. Then use grub's TAB completion to find your partitions.
root (hd0,1) <---this corresponds to hda2
hitting TAB will show you what's in there. When you find your kernel (it'sll be called something like vmlinuz-2.4.20) just leave it appended. then add "root=/dev/YOUR_ROOT_PARTITION" and then do "boot".