All you need to change the Apple Logo & Background Image on the Login Screen in OSx 10.5 Leopard is the terminal and an art program.
If you don't know what the terminal is you should not use it. It is located here: >>Applications>>Utilities>>Terminal and you type in the commands below. ;)
cp /System/Library/CoreServices/DefaultDesktop.jpg ~/Desktop/
sudo cp ~/Desktop/DefaultDesktop.jpg /System/Library/CoreServices/DefaultDesktop.jpg
cp /System/Library/CoreServices/SecurityAgentPlugins/loginwindow.bundle/Contents/Resources/applelogo.tif ~/Desktop/
sudo cp ~/Desktop/applelogo.tif /System/Library/CoreServices/SecurityAgentPlugins/loginwindow.bundle/Contents/Resources/applelogo.tif