Thanks to Marc and the Public Sector Developer Team for this piece of information.  The team offers their method of getting the Windows Aero theme into your Microsoft virtual machine guest operating system, rather than being forced to look at the Windows Vista Basic Theme.

They write:

Have no fear, there IS a way to get the Windows Vista Aero theme for your guest OS.  The trick is to connect to your guest OS from your host OS using Remote Desktop Connection.  Make sure you set the "Experience" to the max when you connect (Desktop Composition & Themes at a minimum):

You also need to make sure you select 32 bit color:

Once connected, you get the full Windows Vista Aero experience:

That’s right! Flip 3D baby! Yes, that’s a WPF application running as well.  You will notice a negligible performance difference. 

What's going on here?  Instead of remoting bitmaps across the wire, data is being passed and hardware rendering is being performed on the client (host os).

To get it, you must meet the following criteria:

• Guest & host OS must be running Vista Enterprise or Ultimate
• Guest & host OS must have the Desktop Window Manager (DWM) Session Manager service running

Read the original, here.