See also the "What is RAID" thread in this section.
http://www.macosx.com/forums/showthr...threadid=20936
Take 2 empty and exactly alike HD's, install, boot. Open Disk utility, and drag the drives (not the logical volumes) to a raid set of your choice. Boom. done.
I did mine with ATA, it may be possible but not advised to do so with removable drives. (firewire)