I just started playing around with this over the weekend and it works great with a straight key. The instructions are here:http://www.mrx.com.au/images/cwcom_help.htm
about 80% of the way down. The quick answer is that if you have a 9-pin serial connector on your computer, go to Rat Shack and buy a female DB-9 connector. Solder two wires to pins 4 and 6, connect the other ends to the key. Configure the software for the com port of your choice and pound away. The site also has instructions for 25-pin connectors and joystick adapters.
If you only have a USB connection, life is a bit more complicated. You can buy a cheap USB mouse and do a bit of surgery, or get a serial-to-USB convertor and use the procedure outlined above.