Communicate Directly With PS/2 or Other Port

I want to create a button that I can press with my foot when my hands are busy. When the button is pressed it will send a message to whatever port it is connected to and my program will receive the message and do whatever it is that I will program it to do.

My question is this:
Does anyone have suggestions as to how I will make this button so that the computer will know when it is pressed, and how can I make my program know when the button is pressed.

I would use a COM port and the MSComm control but I do not have a cable to connect to a COM port. I expect I will need to use a USB port.