Make Screen Saver as Desktop Background
/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background &
This will make your desktop background as your initial screen saver. After you’ve entered that one line of command, Terminal will you the process ID. For example,  478, which 478 is the process ID.
kill PID 478
As shown in example above, the process ID is 478. Therefore, in order to stop using screen saver as desktop wallpaper, the above one line of command is used. Note : 478 is the process ID.
Here is the easiest way to end this : Quitting Terminal.
Cling Dashboard Widget into Desktop Background
defaults write com.apple.dashboard devmode YES killall Dock
With this, you will be able to drag your widget out of your Dashboard into your Desktop. Cool, right?
P.S. This can be used to bookmark useful resource from the web using Dashboard and Safari web clip, except the fact that you cannot scroll down your widget.
defaults write com.apple.dashboard devmode NO killall Dock
The command lines above is used to disable this feature. Actually, the widget can be taken off from your Desktop by simply dragging it back to Dashboard.
For next modification, if you don’t know exactly what you’re trying to do with sudo, don’t risk it.
Change Login Background
cd /System/Library/CoreServices sudo mv DefaultDesktop.jpg DefaultDesktopBackup.jpg sudo cp [drag image] /System/Library/CoreServices/DefaultDesktop.jpg chown root:wheel /System/Library/CoreServices/DefaultDesktop.jpg chmod 644 /System/Library/CoreServices/DefaultDesktop.jpg
These command lines are intended to change Leopard default login background named
DefaultDesktop.jpg with new image file. However, at line 2, we do the backup first by replacing the name of initial login background to
At the 3rd line, you will see there is something like
[drag image]. This portion of command line means that you need to drag the new image file as new login background.
Performing the same lines of command with initial image file will change your login background back.