Microsoft Windows Vista, formally Codename longhorn has a new user interface system codenamed Avalon. This new user interface engine greatly enhances the look by utilizing several cool looking 3D effects. Of course, to be able to fully utilize the new engine you need a good 3D video card on top of special drivers (LDDM).
To turn on this effect just execute c:\Windows\System32\UXSS.exe or enable and start the User Experience Session Management Services.

Currently only ATI Radon 9800's are roughly supported. In order to disable the hardware checking so that you can try the effects on your computer, follow the steps below.

1. Open up Regedit.

2. Navigate thru HKEY_local_machine, Software, and Microsoft.

3. Create a new KEY called DWM.

4. In the new DWM key you created, create a DWORD called EnableMachineCheck.

5. Make sure this value is set to 0 and hardware checking is now disabled.

Quick Note: Although you can get it to run on older hardware, with the lack of LDDM drivers available, it is going to run very slowly!

Source http://www.tweakvista.com/