The technical information from "LEGO MINDSTORMS Internals" ( http://www.crynwr.com/lego-robotics/ ):
Communication
The RCX uses a 38kHz carrier, which is pretty typical for TV remotes. As for the sampling rate, the RCX runs at 2400 bps, which makes each bit approx 417us. Sony remotes (which aren't the fastest), use pulse widths of 600us and 1200us, so we're in the right ball park. I think a learning remote would do pretty well.
Peter Middlestorb reports that a learning remote does indeed work. He used a Casio Model 1174 CMD-40 watch.
Robert Eddings says that the OmniRemote successfully learned and played back the LEGO MINDSTORMS command codes. He has a page with a trained OmniRemote.
Pacific Neotek have released the OmniRemote Development Kit, and RoboRemote, which gives you simple and complete control over your LEGO Scout and RCX MINDSTORMS (like the official MINDSTORMS Remote Control) with an IR-enabled PalmOS device.
The IR protocol associated with sending a "message" to the RCX is pretty simple. Bit encoding is 2400 bps, NRZ, 1 start, 8 data, odd parity, 1 stop bit. A '0' is coded as a 417us pulse of 38kHz IR, a '1' bit is 417us of nothing.
Can I get USB-UIRT to work with this?
(All I need is USB-UIRT to simulate a COM port), is that possible?