I recently bought a Teensy 2.0 and have been programming it to send commands in place of a game controller. (Look Mom, no hands!) As a next step, I'd like to send live commands from my computer to the Teensy. I need to be able to hook the Teensy to the computer while the existing USB port is in use. From what advice I've found, I need a USB serial convertor, right?

I'm mostly concerned with what pieces of hardware I need to get and how to properly hook it all up to the Teensy. I'm not very knowledgeable about these kinds of things (far more a software person), so any help is appreciated.