I'm having problems with VirtualBox on a WinXP Prof 32 bit SP3 host that runs on a notebook with 945GM express chipset and as such GMA 950 graphics. An Ubuntu guest cannot run with 3d gfx acceleration in VirtualBox enabled. The problem is not the GMA 950 hardware, which is (just) sufficient enough to support this 3d mode of VirtualBox for Ubuntu.
According to the community (I didn't test myself) VirtualBox on an Ubuntu host does not give the forementioned problems. The striking reason is that the Ubuntu GMA 950 driver for OpenGL is different/better than the most up to date OpenGL windows driver. The same is a fact for the GMA 950 Mac driver. The Mac driver supports far more OpenGL extensions (see URL http://developer.apple.com/graphicsimaging/opengl/capabilities/index.html).
The main reason of my system not supporting VirtualBox 3d acceleration on host WinXP Prof 32 bit SP3 for Ubuntu guest seems to be that extension "GL_ARB_texture_non_power_of_two" is not supported in the windows driver (see URL http://www.virtualbox.org/ticket/3668). Note that this particular OpenGL extension is supported by the Mac OpenGL driver.
My strong request to Intel is to bring the windows OpenGL drivers for GMA 950 at least on par with the linux and Mac driver counterparts.