Well we are working on a solution, we are building a huge glossary which will explain all of this stuff, we had it ready to go live right before the crash, but it got wiped out as it was a recent change, so we are rebuilding it from scratch.
As for contact closures, check out this page which has more info on magnetic reed switches: http://www.directron.com/reedswitch.html
The gameport is the port on your soundcard, usually used for joysticks. Some people (including me) have written software to read up to 4 button presses, so you can trigger events when a certain button is pressed. But instead of using an actual joystick, we manually wire 4 magnetic reed switches (the kind you use with alarm systems, to monitor doors and windows) to the pins on the port which are normally used for those 4 buttons, so now you can monitor the status of 4 doors/windows/etc ... for little money (just have to buy the magnetic reed switches which are dirt cheap).
As for 1-wire, it is a technology which allows you to connect many 1-wire sensors, usually temperature sensors in the HA world (they are very cheap, you can get some free samples from the manufacture) to the same set of wiring through the house (kinda like a backbone), instead of running new wiring to each seperate sensor. Each sensor has a 'serial #', which is how the 1-wire interface knows which sensor is sending what data. Beside the sensors, you also have to buy that 1-wire interface, which can cost between $20-$100 from what I have seen, depending on the features you desire. Once you have the sensors and interface, using the right software/plugin/script, you can pull the data into your Home Automation software, and put it in a virtual device, have events trigger etc. I don't have any 1-wire devices yet, but plenty of Cocooners do, so hopefully they can chime in or correct me.
If you are serious about interfacing motion sensors, magnetic reed switches and such, I highly recommend investing in an Ocelot with a SECU16 8input/8output module, this is a standalone automation controller, which is much more reliable than using a gameport, and can work with your home automation software to do some pretty cool stuff. Check out automatedoutlet.com if you want more detailed information about this device.