I recently downloaded a screen saver module. When I mounted the image file, the screen saver had the standard .saver extension, but the icon wasn't generic. Could it be that Panther recognizes the .saver filetype? I double-clicked the file and was immediately shown a dialog box explaining that the file needed to be installed first, and would like to install it for one user or for all?
This new installation method certainly beats the old method of digging through the Library folder!
Mac OS X Hints