I guess you could run something like Remote Desktop, so that your laptop would control the tower, but short of that, no. And you won't be impressed by the latency/lag of remote desktop, or the graphics quality. It would work in a pinch, but you probably wouldn't want it as your "daily driver."
something I'm not quite following - why would you want to do this? The powerbook is going to be a faster/better machine than the tower... so what's the benefit?