How can I enable the Windows Vista Basic UI and (if the hardware supports it) Windows Aero on Windows Server "Longhorn," code-name for the next version of Windows Server?
By default, Longhorn doesn't contain the Vista Basic and Aero schemes; however, you can install them into the OS (along with Media Player and Photo Gallery) by installing the Desktop Experience Pack. To install the pack, follow these steps:

1. Start Longhorn Server Manager (Start, All Programs, Administrative Tools, Server Manager).
2. Select the Features link in the console tree.
3. Click the Add Feature link, as Figure 1 shows.
4. Select Desktop Experience and click Next.
5. You'll see a list of features that will be installed. Click Install.
6. Once installation is complete, you'll be prompted to reboot.

After rebooting, if you right-click the desktop and select Personalize, you'll notice that the Vista Basic and Aero schemes are still not available. That's because the Themes service is disabled by default on Longhorn. Perform the following steps to enable the Themes service:

1. Start the Microsoft Management Console (MMC) Computer Management snap-in (Start, All Programs, Administrative Tools, Computer Management).
2. Expand Services and Applications in the console tree and select Services.
3. In the details panel, scroll down till you find Themes, rightclick it, and select Properties.
4. Set the Startup type to Automatic, as Figure 2 shows and click Apply. Click Start, then click OK.

If you now select Personalize, then select Windows Color and Appearance, Vista Basic will be available. If your server has hardware that meets Aero requirements (which is unlikely), you can also select Windows Aero and get access to taskbar thumbnails and Windows Flip 3D graphics technology, which renders live thumbnail images of the contents of your open windows.
—John Savill