dirtshell:
whoa whoa whoa, so what is this talk about resistors. I dont understand how you would set this up. So you cant just use the pins as GNDs? The easy way to do this is to setup some pins that act as virtual buttons. But this would require double the number of buttons (15+).
Yes, you can just use the pins as grounds although it is rather a waste since you might just as well connect whatever you want grounded to the Arduino's ground. In terms of switches connected to Arduino input pins you can arrange the hardware so that the switch pulls the input high, or so it pulls it low.
The point of using resistors is that you can connect multiple buttons to a single Arduino input pin by connecting each pin through a cunningly designed circuit that produces a different voltage for each possible combination of buttons pressed. If you're running out of pins, you might consider that. If you aren't, you don't need to worry about that.