Google should be able to give you the info on how to connect a switch to a serial port.

A search of CPAN for SerialPort gives 25 results but not all are applicable. Look at Device::SerialPort, Win32::SerialPort, Win32API::CommPort or perhaps even X10.

I wish that I had time to play\Wwork with this sort of stuff.

Update: Fixed my http://search.cpan.org url.