Infared Networking with Windows 98
Interfacing two computers with infared is pretty easy after all. Just by pointing the infared ports at one another, the systems are automatically identified and given transfer icons. What might be interesting, and I don't know if IrDA or IrDA-compliant infared devices allow it, but if you could directly program the waveform that goes out of the infared port, it'd be interesting to see what other kinds of modulation you could apply. (might be an interesting project to pursue in Linux)
From what I've heard, one of the possible physical (PHY) layers for 802.11 was infared, although sticking to RF was a much better idea.
Anyway, here are some screenshots from the connection: