Optiplex 755 & Raid0 using Intel Matrix Storage Manager

I've recently purchased a new Optiplex 755, which came with two 250GB H/D's running VISTA.

The PC came pre configured with RAID1

 

I would like to reconfigure with RAID0 (I've wiped everything) but I don't seem to be presented with any option for RAID0.

 

Ideally I'd like to add a 3rd disk and use the Matrix Storage Manager to go part and part with RAID0 and RAID1 as per the documentation for the ICH9R on the Intel web site.

 

Have Dell "prevented" the Optiplex 755 from using RAID0, does anybody know? It would seem a bit odd as it pretty much makes the benefits of Matrix redundant!