With "Processing" and "firmata" you can control the Arduino from the computer. The program you write runs on the computer and the Arduino is like an extension to the computer.
http://playground.arduino.cc/Interfacing/Processing
The CapSense library is similar to MakeyMakey.
http://playground.arduino.cc/Main/CapacitiveSensor
I have my doubts about resistors in line and alligator clips. With a 9V battery around, a mistake is easily made and the Arduino gets broken.
A complete shield with sensors would be easier. Or perhaps something like the tinkerkit, sensors can be plugged in.