Are you not a big fan of the new login wallpaper in Leopard? I wasn't a huge fan either and luckily, there is a pretty easy way to change it, and I'll tell you, and show you, how. Just a disclaimer, I am NOT responsible if you screw up your Mac in any way, shape or form. This process worked for me and it should work for you. Also, CoreServices contains some important system stuff, so if you don't know what you're doing, don't do it. Watch the screencast.

  1. Navigate to the CoreServices folder which is located at Macintosh HD/System/Library/CoreServices.
  2. Once you are at the folder, you may want to make yourself a read/write owner of the CoreServices folder. To do that, do a Get Info on the folder (command + I). Expand the Sharing & Permissions section. Click the lock icon and enter your admin password. Click the plus (+) button, a window will pop up. Click on your user and click Select. Change your permissions to Read & Write. Now you are free to do any modifications to the CoreServices folder without authenticating each time you try to make a change.
  3. Now, what I would do is compress the DefaultDesktop.jpg file and keep that archive in the CoreServices folder so you will always have it.
  4. Now, replace the DefaultDesktop.jpg with another image with the same name.
  5. You may now want to take your permissions away from the CoreServices folder, to do that just select your user name and click the minus (-) button and you're good to go.
  6. One last thing, open up Disk Utility, select your hard disk and run Repair Disk Permissions. This may take a while (it took my Mac about 5 minutes). After Disk Utility has finished repiaring the permissions quit Disk Utility.
  7. You are now good to go. You can log out and you should see your new Login screen wallpaper.

Added December 17, 2007: Another, much easier way to do this is to use Desktop 2 Login. Set the picture you want to use as your login wallpaper and run Desktop 2 Login.