Oh, btw, how to send a serial data stream and modulate it onto a 38Khz 'carrier' frequency?
Well it can be done by ANDing a 38,000hz square wave (maybe from a 555 timer chip) with the serial transmit output pin.
A possible minimum component solution (it would depend on the current requrement of the IR emitter) would be to wire the cathode of the emitter to the serial output pin of the ARduino the other end of the emitter to a series current limiting resistor and the other end of the resistor to a Arduino output pin that is programmed to output a continous 38,000 square wave. You have to size the resistor such that the current is limited to 40ma or less.
Lefty