The new CoreAVC now has hardware decoding via CUDA, so i might ditch the ATI card and pick up a cheap nV one, and give it a go - should hopefully have no need for EVR then.
In Vista EVR is recommended renderer as you don't have to use the exclusive mode (that has few limitations). As VMR9 is not the recommended one it might have more issues than the EVR implementation in MP.
Quick question, is there anyway to get MP to use Haali Renderer?
No, would require additional code to support haali renderer.