OS: MAC OS 10.5.7 Verified
This Script is Called: Leopard Login Screen Changer.
What It Does: Changes The Boring Galaxy Image off from your Login Screen in OS X Leopard to the Image you love.
Is This Script Really Useful: Naa, Just some Eye Candy.
Any Damage To My System: Nothing serious, After Running the Script for the first time Backup and Keep that DefaultDesktop.jpg file which gets created in your Desktop.(As Later runs will Replace that File with the one you selected previously.)
Any Further Improvements: Possible, But time frame cannot be set.
Which Image I can Set: Only .jpg files

Where can I Get It: Download it From Here

Well, Got listed in Softpedia....

http://mac.softpedia.com/get/Utilities/Log...n-Changer.shtml