Dream world technology: Does this exist?

Background : I have a laptop running a triple boot of Windows XP, Windows Vista, and Ubuntu -Hardy Heron. I also have an Apple G5 running Leopard. I’ve got a monitor with a DVI adapter and a usb keyboard, mouse, and external hard drive. Currently the two systems are completely separate and I have to move the external hard drive back and forth for all of my media.

Ideal: I want to connect both of these machines to some sort of switch or hub thing, that would allow me to use the monitor, keyboard, mouse, and external hard drive for both the laptop and the mac. Ideally, when using the laptop, the monitor would act as a second monitor. [And in an ideal world, while using the mac, the laptop screen would function as a second monitor, but I doubt that’s possible].

Question: Is there any piece [or pieces] of hardware that do this kind of thing? If so what is it called, ie what should I search for online?