Usually the IR port off of cable boxes are for transmitting a signal to say a VCR. So the cable box tells the VCR to turn on, record etc. If you want to control the cable box you need a IR transmitter from the PC aimed at the cable box. I'm not sure about the software required to make the above IR trasmitter to work with MCE, but I'm sure you can find it here or a google search. One I know of is called girder, difficult to learn, but effect software.