Touch screen advice

I'm planning to start some studies that would require a touch screen. I'm mainly interested in getting the position of the finger while it is pointing on the screen, but I would eventually be interested also in tracking the finger movement on the screen.
I would like to get some advice from those of you that already use a touch screen in combination with PTB and running Mac OS X.

Any suggestion about a particular model?
Is the finger position on the screen actually extracted in the same way as the mouse position?
Do I have to anticipate particular problems?
It would be nice if the touch screen could be used also in an experimental setup with monkeys.

Many thanks for any advice.

Viktor