Creating 2d nodes is not very different from creating normal 3d nodes.
You must just create a file named "2d.jpg" in the node folder. This file must contain the picture of the 2d node. It should be a picture set to the final game resolution i.e. if your game will be 1024x768, you must create a 1024x768 picture. In fact, you can build and launch the game in an other resolution, and the picture will be stretched, but the game will be a little more slow.
To create "mechanisms", you must always use right mouse button in the game, to get "clickX" and "clickY" values. In the data.xml file the code should be like that :
<mechanism clickX="0.0056" clickY="0.998" clickRadius="0.5" sound="1">
You can also create widgets, using "widget" marker without "skyboxPart" parameter, like that :
<widget widgetPicture="widgetfile.bmp" posX="10" posY="10" />
but there is currently a problem with the widgets : the widget position will depend from which game resolution you use.