would it be possible to have two? one in the standard location and another facing out the back of the screen

On a Powerbook G4 15 inch Aluminium screen module, I don't think there is even space for one in the standard location, due to the location of the latch. You would probably have to mount one off to the left or right of the latch, and mount the other one on the opposite side.

Photobooth can handle two iSights connected though (well, I've only tested with one firewire + one USB), it lets you switch between them with a control that is only visible if two are present.

I'm thinking of adding an isight to my ibook(if I can figure out a solution for the latch), does anyone know the pinout for macbook, imac or macbook pro isight.

I would look into this as well.

If the isight camera is connected via a usb cable built into the macbook pro model laptop then you should be able to take it out of one machine and move it to another by just wiring the wires to the internals of the other laptop.

But if it isn't a usb cable and some sort of ribbon cable which we know apple loves to use you might be in trouble.

I haven't take apart a MacBook Pro, but a macbook isight is connected via USB that is part of the video data cable, which isn't FFC, but micro-coax.

I can get these pinouts. It will take a little time is all. The MacBook Pro iSight cable comes all the way through the hinge and has its own connecter on the board unlike the MacBook which is part of the LVDS. I was going to do the same mod two years ago to a G3 Lombard PowerBook before it got stolen.

Has anyone succeeded in hooking up an internal isight to an external USB on a mac or pc? I'd appreciate any pointers.

For things to be cheaper you don't have to use a isight camera. I have a cheapy Philips laptop webcam that I stripped down. I used this in my Dell mini 9 laptop. My laptop had enough room to fit a small Belkin 4 port USB hub. I had to desolder the USB connectors and hardwire everything. For the wiring to the webcam I used some packaging tape and some gold foil from a hobby shop, I created a 4 pin cable out of it and ran it from the USB hub to the webcam's circuit board. This gave clearance for the display hinge.

Right now i'm currently trying to find a spot to add a USB port because with the HUB that will only let me use 4 USB devices internally im stuck with one external USB. I might just build myself a docking station.