Maybe I have interpreted it wrong but I thought that this command limited access to the grub menu.
Sorry Vasco, I thought it would too. Kind of pointless otherwise...
Wait, from "info grub":
password [`--md5'] passwd [new-config-file]
If used in the first section of a menu file, disable all
interactive editing control (menu entry editor and command-line)
and entries protected by the command `lock'.
So, you just have to 'lock' the entries.