How do you install a screensaver onto the Login Screen?

[SRAMTRC at windy.dsir.govt.nz]

Does anyone know how to install a screensaver onto the Login screen? If you
haven't tried it, it is not as simple as installing, say After Dark,
into the Login System Folder. I tried that and it works fine. The Login
screen has its screensaver which works. But the problem is that when you
try to login you can't. All attempts to log in result in a return to the Login
screen. Funny Stuff!

Cheers,
Tony Cooper
sramtrc at albert.dsir.govt.nz