Another option is to replace the two 160gb (the ones in RAID-1) with bigger drives.
You can replace them one at a time (allow array to rebuild inbetween).
This will give you extra space in the array that you could use to offload the data from the single RAID-0 drive.
Note that (unfortunately) in order to utilize the new space (expand array) you will ALSO need a FBWC/BBWC module added to the controller, so either way, you need to spend some ca$h.
You could then re-use one of the 160gb drives to convert the RAID-0 array to a RAID-1, to add data security ;-)