What I do is have swap on each disk. Mirror /boot and /. After your install is done, su then 'grub':
grub> device (hd0) /dev/hda
grub> root (hd0,1)
you will get a message describing your file system.
grub> setup (hd0,1) [you might not need (hd0,1) here]
Then do hdb. To make sure it works, shut off your machine, unplug hda and see if the machine boots. I'm doing this off the top of my head ( I don't have my cheat sheet here) so take the code with a small grain of salt
This way if hda dies you can still boot normally without having to use a cd or boot floppy.