Windows 7: Dual screen, 1080p as secondary monitor, theme issues

Hi,

I've been having issues with windows 7 aero themes. I run dual screen one running 1440 x 900 and the other running 1920 x 1080. I want the smaller screen to be my primary monitor but when it is set as such the aero theme (currently set as the UK theme) does not fill the larger screen (there is a black border surrounding the image). When the larger screen is set as the primary, the theme does fill the screen. My graphics card is a nvidia geforce 8600 gt and is connected to the larger screen (which is full hd) via dvi to hdmi.



The nvidia control panel has an option to stretch the screen but going on this the application says the desktop should fill the screen so I'm guessing the problem lies with the aero theme and not the graphics card.

Any help would be much appretiated and any further information can be provided.

Cheers

Bunter