well I sort of hacked an existing graph to make it 3d. it seemed to work for the most part - this is the first time I have done anything in 3d. I just took any lines that were calculating co-ordinates in the x and y direction and tacked on a z. There were a couple places where I had no idea what to do, and this is why I'm writing...

1. for the following, how do you specify "depth"?
 void update () {
   if (!fixed) {
     x += constrain(dx, -5, 5);
     y += constrain(dy, -5, 5);
     z += constrain(dz, -5, 5);

     x= constrain(x,0,width);
     y= constrain(y, 0, height);
     z= constrain(z, 0, height);
   }
   dx /=2;
   dy /=2;
   dz /=2;
 }

2. Again, I think I need a "depth":

Node(String common) {
   this.common = common;
   x = random(width);
   y = random(height);
   z = 0;
 }

3. There doesnt seem to be a built-in mouseZ:

void mouseDragged() {
 if (selection !=null) {
   selection.x = mouseX;
   selection.y = mouseY;
 }
}

any ideas?