Firstly, make sure your in Path Mode...
Click on P to bring up the Path Panel, and from that click on the "Game Paths" radio button.
Now click on the viewport you wish to begin in, and pick the place you want to place the first node. To lay down the first node, press CTRL+SHIFT+Insert.
It will then prompt you for a name, give it one, then hit okay. Now you can drop further nodes as if you were dropping verts, just by pressing insert... and they'll be connected too
