Automatic Shutdown

I need to find a way to shut down my Linux PC (Ubuntu 8.04 Server) after it has up & downloaded 100MB.
Anyone has any idea on how to do this?

EMACS question: how the hell do I set faces? Say I've been provided with a hl-line-face, how to set it to "red"? (setq 'hl-line-face "red") gives me a type error.