The state of HDMI Consumer Electronics Control (CEC) interfaces for PCs seems pretty dismal. Neither ATI or nVidia currently have CEC support built into their graphics devices with HDMI interfaces. So you can’t directly send or receive CEC data over the CEC-line (pin 13/17).
One bright spot is the RainShadow HDMI-CEC to USB bridge/converter. Supposedly it’s also been hacked into a regular video card. While it's not a direct HDMI CEC interface for a PC a Raspberry Pi with Pulse-Eight's libCEC could provide control over a network connection.