I don't think the N900 got an IR receiver you can use, but look it up on the internet there should be instructions on how to build an IR transceiver you can plug on the mic and speakers plug of a PC soundcard (or you could even use somthing like a tape recorder or MP3 player with recording functions and transform that into an universal remote), it should be just a matter of adaptng the cabling for the N900 headset plug.