Here's and easy one to do, and quite enjoyable.
to change the boot screen in OSX replace the file "BootPanel.pdf" in the Folder "System-Library-Core Services-Resources" with a 640x480 pdf picture renamed "BootPanel.pdf"
To change the login screen, replace the "loginpanel.tiff" in "System-Library-Core Services-loginwindow.app-Reources" with a new 400x320 tiff image renamed loginpanel.tiff
Then reboot. A great resource for this is http://www.macAkio.com/
enjoy
to change the boot screen in OSX replace the file "BootPanel.pdf" in the Folder "System-Library-Core Services-Resources" with a 640x480 pdf picture renamed "BootPanel.pdf"
To change the login screen, replace the "loginpanel.tiff" in "System-Library-Core Services-loginwindow.app-Reources" with a new 400x320 tiff image renamed loginpanel.tiff
Then reboot. A great resource for this is http://www.macAkio.com/
enjoy