sure. usually whatever raid array you buy comes with software to do it. or i'm sure you can buy 3rd party stuff. i had a buddy that had a scsi one way back.
Mac OS X Disk Utility and SoftRAID can do RAID 1 (mirror) or RAID 0 (stripe). Main thing is to make sure the drives are the same size/speed, otherwise the smaller/slower of the 2 will be your limiting factor. Also, Firewire is preferrable to USB 2 as the sustained rate and performance will be much better.