I am branching out for help on this into the PC world.

I am running a 2008 MacPro that boots into VISTA. I have two external eSata hardrives. Vista sees the drives and can format the drives. However. My entire goal is to do a raid 0 for a fast "read" drive for media, uncompressed 2k files and hi res HD quicktimes.
So my PCI card is working, drives show up.
When I go into manage the disk. I can create a new stripe. choose both 500gig drives and choose to raid them. When I execute the command I get an error every time saying, "there is not enough space on your disk to complete this operation"
I have tried creating a 1T raid, a 500gig raid, a 20 gig raid. No magic number works?
Is it strange that VISTA will not raid these drives?
Any thoughts or ideas. I really need to get this raid up and running.