Have you seen this article on our website which describes how to interface a simple mechanical coin acceptor?
http://www.breezesys.com/articles/ph...n_acceptor.htm

It works by using a script which puts the booth into standby mode after each set of shots and using the signal from the coin acceptor to switch to ready mode. The arcade style start button will only work when the booth is ready and will be ignored when it is in standby mode. This technique can be modified to work in different ways e.g. if you have a coin or bill acceptor that interfaces to the PC and updates a log file when money is accepted the script could be adapted to read the log file instead of waiting for a key press from a coin mech connected to a StealthSwitch.

BTW the latest versions of the software allow you to play a movie file on each screen and so you could have a movie file named welcome_loop.mov that is played continuously when the booth is in standby mode rather than just displaying a static welcome.jpg screen.