There's this cool new feature of Apple's new operating system (Leopard) called "Back to my Mac" where you can share screens. So, here is the screen from one Mac on the screen of the other Mac (does that make sense?).
Now, I don't really know why you need to do this - but, hey, it's so much fun!
(And - you can just drag things from one computer to the other without using firewire. Now THAT is useful!)