This topic is a how to. Please keep it as clear and simple as possible. Avoid speculative discussions as well as deep dive into underlying mechanisms or related technologies.

(what is this box?)

Desktop Composition is a screen drawing mode introduced in Windows Vista. Aero Glass Visual Themes require this feature. It is disabled by default for Remote Desktop sessions for performance reasons. However, if you use Remote Desktop Session Host (ex-Terminal Server) and VDI scenarios where remote machine (either server or virtualized workstation) serves as a replacement for a desktop PC, you can enable it.

Before you enable Desktop Composition for Remote Desktop sessions

1. Client computer requirements. Your client computer (the computer on whish the “Remote Desktop” client software is running) must already support Aero Glass.
   • This means that in-box video drivers shipped with Windows Server 2008/R2 will not work. Use a client such as Windows 7 or install the driver package from your server hardware vendor. (They all are designed for client SKUs but work fine on servers).
   • Aero Glass Visual Theme may be or may not be enabled on your client computer.
   • Supported OSes are Windows Vista, Windows Server 2008, Windows 7 and Windows Server 2008 R2.
2. Connection requirements.
   • You must not use /admin command-line switch when starting “Remote Desktop Connection” client application. For more information on this command-line switch see Microsoft Support Knowledge Base Article 947723 “Changes to remote administration in Windows Server 2008”.
   • Set “Desktop Composition” check box on the “Experience” tab of “Remote Desktop Connection” client application.
   • User 32-bit per pixel color depth (“Highest quality” setting) when connecting. You may need to make sure this setting is enabled/accepted both on server and client sides (see “Links” section in the end of this topic for detailed instructions on this).

3. Remote computer requirements.  The remote computer means the computer you connect to with the remote session. It may be Windows Server with Remote Desktop Session Host server role enabled or a client computer OS. It doesn't matter if they are running on hardware or in a VM. No special hardware is required. For example, the remote server could use an old graphic card (not Aero-capable) with default inbox drivers.

To enable Desktop Composition on a server OS:

1. Enable the Remote Desktop Session Host server role. 
2. Install the  “Desktop Experience” pack.

   • • Open Server Manager: click Start, point to Administrative Tools, and click Server Manager.

       • NOTE: You can also open Server Manager by typing the following at a command prompt: servermanager.msc

     • In the Features Summary section, click Add features.

     • Select the Desktop Experience check box, and then click Next.

     • Complete the wizard by clicking Install.

3. Enable and start “Themes” service and set it to automatic startup mode. 
4. Enable the following Group Policy setting: Computer Configuration → Policies → Administrative Templates → Windows Components → Remote Desktop Services → Remote Desktop Session Host → Remote Session Environment → Allow desktop composition for remote desktop sessions
   • There's no special hardware requirements. So the server side could use an old graphic card (not Aero-capable) with default inbox drivers.

NOTE: Windows Server 2008 is not supported. Supported server OSes are Windows Vista, Windows 7 and Windows Server 2008 R2.

What will not work with Desktop Composition and Aero Glass Visual Themes in Remote Desktop sessions

1. Virtual Machine Connection (VMConnect.exe) application (for Hyper-V VMs). You always need to use Remote Desktop Connection client application to make Desktop Composition work with Hyper-V VM.
   • Windows Virtual PC (WVPC) connection (VMWindow.exe) does work though (see “Links” section in the end of this topic for deep technical explanation). Integration Features must be enabled for this.
2. RemoteApp. You need to use full Remote Desktop Session experience.
3. Multiple monitors for single Remote Desktop Session.
4. Mixing Client and Server OS Generations. Both Server and Client must be either Windows 6.0 (Windows Vista and Windows Server 2008) or Windows 6.1 (Windows 7 and Windows Server 2008 R2). See “Links” section in the end of this topic for support matrix.

Links

• Aero Glass Remoting in Windows Server 2008 R2 (Remote Desktop Services (Terminal Services) Team Blog)
• Aero Glass? In my Virtual Machine? It’s more likely than you think… (“Virtual Varia”, Mike Kolitz's blog)