the guest operating system doesn't see your real hardware, only the virtual hardware. Installing the guest additions adds everything necessary for hardware drivers (except for USB devices you might use in it...)
Have a look at my Virtualization References and read a few. Your VM does not have an Intel 946gz GPU. Your real machine has the Intel 946gz GPU. If you want to use it then dual boot your OS. Your virtual machine has a virtual graphics chip which gives basic VEGA functionality -- enough to drive windows, but not 3D games.