That would be the /System/Library/CoreServices/SecurityAgent.app/Contents/Resources/loginpanel.tiff file. So to replace your login screen, you would do the following. I don't know your level of expertise, so i'll try to keep the directions simple:
1)Download and decompress the desired file
2)In the terminal, type 'cd /System/Library/CoreServices/SecurityAgent.app/Contents/Resources/' (without the quotes)
3)Type 'sudo cp loginpanel.tiff loginpanel.tif.bak' (again, without the quotes). This will make a backup copy of the current image.
4)type 'sudo cp /[path to downloaded file]/loginpanel.tiff ./' (no quo... ah, you get the idea
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
) Replace [path to downloaded file] with the actual path, or you can just drag the downloaded loginpanel.tiff file into the terminal window after typing sudo cp, and it will be filled in for you.
That's it. Log out, and you should see the new image in the login window. However, depending on the size of the image, it may be cropped somewhat. If this is the case, hopefully the download also included a file named "login.nib". This file would then need to be placed in the directory /System/Library/CoreServices/SecurityAgentPlugins/loginwindow.bundle/Contents/Resources/English.lproj/ This can be done using the same procedure as outlined above for the loginpanel.tiff file, but you would need to replace the path listed there with this one, and where before you typed 'cp', you would now need to type 'cp -r' (since it is a directory as far as the terminal is concerned) For the most part, these directions should be included with the downloads, however as you are in 10.2, the directories listed in the downloaded files may be incorrect. Those listed above should work.
I hope this helps. Good luck, and be sure to post again if anything is unclear.