Hi Shari,
I'm not familiar with that particular shopping cart but breakng up payments is usually something that has to be custom coded into a cart - at least I've never seen it as a standard feature on an out-of-the-box cart program before.
I took a look at their info and didn't see anything even close to relative to what you're looking for - just basic Q and A, which leads me to believe it's a pretty basic cart system.
Have you tried giving their support a quick call - there's a support phone number there in the cart info section...might be your quickest route to a final answer.
Good luck with this!