RAID 0 is stripping - that mans you get all the disk space, fast access but no redundancy. In a nut shell if you loose one disk ALL your data is gone.
If it has to be a RAID then would favour a RAID 5 array with the x3 320GB drives.
RAID 5 needs at least three disks. You only get the storage capacity of two of the disks i.e. 640GB (less the normal loss attributable to manufacturers quoting 1000 bytes as a KB as opposed to the actual 1024) but you get redundancy. If you loose one disk simply put in a new one and the RAID will be rebuilt and you have lost no data.
All that said just getting a 500GB single disk and having an external drive to back up your valuable data to, would do the job without all the hassle of setting up a RAID.