you need to switch boot order to boot from USB if your mobo allows you such an option
but you gotta load software onto the drive so that when the BIOS tells the drive it needs to perform a task, it runs how you wanna do it
your mobo or hd controller will come with raid software support upon boot, ask you to put it on a flop drive, but instead put it onto your usb drive and boot from usb device
otherwise, hit up screwegg.com and cash your 5 bucks plus shipping for a flop drive
you could try a raid build on another comp and carry it over, but if your mobo dun like the array for the controller supported options, you're vucked.