Connecting Two Displays to MacBook Pro

Connecting two monitors to a MBP isn't hard; what will be difficult about the demonstration you contemplate is giving the students any idea what you're doing on the Cintiq to cause what they'll see projected. If the demonstration is to be more about using Photoshop itself than about using the Cintiq with it, it will be much more effective.

The Cintiq needs a DVI port (or a mini-displayport-to-DVI adapter) and a USB port for its own use. The simplest way to connect the projector, if it has a DVI-in port on it, would be to use a USB video adapter such as the Villagetronic ViBook (there are also other, similar devices on the market). If the projector has only a VGA-in port, check with Villagetronic or the manufacturer of any other USB adapter you're considering to make sure you can use a DVI-to-VGA adapter with it, or look for a USB video adapter that outputs VGA directly instead of going through DVI. Such an adapter may be limited to lower resolutions than one that outputs DVI, but that shouldn't be an issue if the output is to a projector, because projectors generally have lower resolutions than monitors.