The IR543 is a device manufactured by X10 that sends out a X10 signal in response to a IR commands, they run about $20 and are limited to 5 unit codes (1-5 or 5-10) and one house code (a-p).
Over on the X10 chat I have been telling folks about a new device I discovered that can send out any X10 command (multiple unit and house codes) when it receiver any IR command. It learns a IR command and then you associate it with any X10 command. It can learn up to 27 IR commands with associated X10.
I think it is cool, and is much smaller and better looking than the IR543.
Bill
www.homeautomationnet.com