It should be able to do this...

What specifically 'is not supported' - what are you trying to do?

Different graphics cards will work in different ways - you should not assume that new hardware will identically to old hardware.

There are a number of things that need to be configured for catalyst to work successfully on any MacPro, not least the new 5,1 (2010/2011) Mac Pros. Its not a simple case of unpacking the box and expecting it to work flawlessly...

Tell us what you need to do - and we can try to help

S