Using two identical external drives to create redundancy?

I have 2 500GB external drives that I want to use to backup some important, non-sensitive, data on. I only roughly 400GB of space, so I want to setup some sort of raid system that lets me use both drives at once, but that won't loose data if one of them should fail.

Is there any way to do this in Leopard? If so, how?

EDIT: Oh, and I'm running Leopard Server on the machine.