You need an IR blaster. That's a device controlled by HTPC media software to control external devices. There are a number available from independent makers and also DIY kits/instructions. Some versions of the MCE remote have them built in. Some TV tuners (Hauppauge) and capture devices have them as well. Many are made to control a single device, the cable/satellite tuner, but some can control several devices by using the appropriate software. I use an IR blaster to control the satellite receiver and a Harmony remote to handle TV and other device functions.