i built an internet garage door opener/closer out of a few spare bits. here's what.
A serial port has three binary lines you can read (CTS,DSR,CD) and two you can write (DTR,RTS).
I used the DTR to drive a transistor and a relay (12v for the relay was taken from the PC's power supply). The other side of the relay "piggybacks" onto the switch on the wall which controls the garage door.
A little C program opens the port, engages the DTR line for 0.5 seconds and then disengages it. This is equivalent to pressing the button on the wall, and opens/closes the door.
For reading the position of the door I bolted a piece of cardboard to the chain which drives the door up and down. It slides into a slot optocoupler, which is then read by the CTS line of the serial port. Another C program opens the port, checks the status of the CTS line and reports TRUE or FALSE.
To put it all on the web, I installed apache server on my linux box, wrote a simple PHP script with a button to open/close the door, and a piece of text which tells you the status of the sensor.
I found a password-protecting PHP script on the net, configured my router to port-forward to the web server, and got a dynamic DNS from no-ip.org. Now I can access it anywhere!
the picture shows the top of the opener mechanism. You can see the piece of cardboard bolted to the chain in the bottom of the picture. There are two sensors: one for "open" and one for "closed" although I only use the "closed" one at the moment. at the moment you can see the cardboard interrupting the slot opto for the "open" postition.
The prototyping circuit board contains a few resistors and stuff for generating a 0-5v logic level from the output of the slot sensors.
It took me about 5 hours to figure out how to do it, and build the whole thing. Cost: about £5.
The good thing about slot optos is that you can put them anywhere on the door, all you need is some kind of attachment to the door which slides in between the emitter and sensor. An alternative would be to use a webcam, so you can see whether the door is open or closed. I didn't have one hanging around, so I went with the slot opto idea.
good luck ! let me know if you need any help. I can give you code, schematics etc.