Remote control an arcade machine with Arduino

I'd like to remote control my arcade machines using my computer and arduino. What sort of setup am I looking at needing for this?

Is there a way to trigger say... pin 2 on the arduino which could then somehow credit my arcade game? The arcade game is just using an open/close circuit with 5v running to it to detect a credit. Same sort of scenario with the joystick/buttons.

So how could I send a command to the arduino via serial port to then trigger the circuit to be open or closed on the game hardware? Would I need a relay setup?

Any help would be greatly appreciated. Thanks!