virtualbox.org

I have a Windows 7 host (Corei7, 8GB RAM, dual monitors) and guest (2 CPU, 2GB RAM, 256 MB video RAM). The guest is configured for dual monitor support. I have installed VB 4.1.0 and the 4.1.0 Guest Additions with the WDDM video driver. When I enable 3D acceleration and dual monitors for the guest, the guest is very slow to respond and if I resize one of the virtual monitors, both virtual monitors display black. Eventually the Windows desktop is displayed, but then the mouse does not work. If I disable 3D acceleration in the guest and enable dual monitors, the guest works fine. Also if I return to a single monitor and enable 3D acceleration all appears to be fine.

Guest monitor resolutions are 1920 x 976 and 1920 x 1016.

I looks like the guest needs more video RAM, is their anyway to give the guest more video RAM so that it will run Aero in dual monitor mode?

I am not surprised. This is the first (experimental) release of the WDDM driver. I would not expect it to handle that sort of setup yet.