well, i did it with lilo, I don't remember how.
but when u have lilo, and not grub, you can set activate a drive #lilo activate /dev/hdblabla (I think), and then something with lilo.conf i suppose, I don't remember many things, as I did it a long time ago. and now I installed freebsd, and messed up the thing.
so good luck
its easy I suppose
just search info about lilo