The piezo on the Toytronic FB game (http://www.seanriddle.com/toytronicfb.txt) is hooked up like this: RC6 is tied to VDD with a 3.3K resistor, and also goes to a 0.04uF disc cap. The other end of the cap is connected to the cathode of a diode and to a transistor's base. The diode's anode and the transistor's emitter go to VSS. The transistor's cathode goes to a transformer; the other side of the coil goes to VDD. One side of the 2nd coil goes to VSS and the other side to the piezo. The other piezo connection goes to VSS.
The other football game (http://www.seanriddle.com/football.txt) has a simpler piezo circuit. RC6 is tied to VDD with a 2.7K resistor, and also connects to a transistor's base with another 2.7K resistor. The transistor's emitter goes to VSS, and the collector goes to the piezo and to a 10K resistor. The resistor goes to the other piezo connection, a diode's cathode and a 4.7uF electrolytic cap's positive side. The diode's anode goes to VDD and the cap's negative goes to VSS.