Yes, using "over-ride Skin theme with Windows System Theme" will allow MM to make use of the full screen.
Monitor placement is set to  , with MM open on screen 2.
Interestingly, if I switch over as tommycrock advises, so that MM is on screen 1, and the Windows Taskbar is on screen 2, then MM4 is able to utilise the full screen space. I only use the multi-monitor tool at work, while at home I am not using anything more than windows native. The issue affects both systems the same.
I'm using an ATI video card purchased new at the beginning of 2010 (although still using AGP slot), with two monitors connected via DVI ports.
As to ASIO, I forgot to mention that WASIONA does not work at all - as it still crashes as soon as the "configure" button is pressed. I've sent in MM's error reports (using debug version)