This is not a "must have", but it is a lot of fun. You can play a video as desktop background which is especially nice if it is a music video.
For that you need VLC. If you do not have it yet, you can install it from e.g. here ( Download VLC Media Player 1.1.2 - FileHippo.com ). And here are the few easy steps:
1. Open VLC and go to Tools > Preferences
2. Click on the icon called Video on the left (3d icon from the top)
3. Change Output (which is set to Default) to say Directx Video Output
4. Click on the Save button (important)
5. Now select the video you like to play -> Media > Open File
6. Right click on the VLC window where the video plays and go to Video > Directx Wallpaper
7. Minimize the VLC window and enjoy your new desktop.
If you want to get out of it, right click on the VLC icon in the taskbar and Close VLC. In case you later want to use VLC for "normal" operation, you have to reset the Output to Default and Save it.