simple device that connected to the computer serial-port enables the reception of infrared codes emitted from any commercial remote control unit and with a little Windows program.
http://www.pcremotecontrol.com/circuit.html
http://www.howstuffworks.com/inside-rc.htm
simple circuit which controls one relay output.
http://www.aaroncake.net/circuits/irremote.htm
http://www.mitedu.freeserve.co.uk/Circuits/Interface/irext.htm
http://www.mitedu.freeserve.co.uk/Circuits/Interface/irext2.htm
http://www.mitedu.freeserve.co.uk/Circuits/Interface/irext3.htm
with information about computer interfacing.
http://www.epanorama.net/documents/ir/irremote.html
Coder decoder uses MC145026 and MC145027 pair from Motorola
http://www.boondog.com//tutorials/lrir/mc145026.htm
Interesting project that creates an extended tethered remote control using an XBox controller complete with a small LCD screen.
http://www.ghettohardware.com/articles/mcebathroom/
http://www.eddiem.com/projects/Pir-remote/pir-remote.htm