You need to reference the instance of the Form1 object, not its class.
So in Form2, delcare a Form1 object. Then, when you make a call to open Form2 from Form1, set the Form1 object that you declared to point to the instance of Form1.

I know how to highlight a treenode when the mouse is moving over it in a drag and drop, but what I would like to do is change the forecolor of a node and change it back when the mouse is moved away from it - sort of like when a link turns blue when you hover over it.

The difficulty lies with the absent of a node mouseEnter and node mouseLeave event. Without these, there isn't a way to detect when the mouse has moved over to a different...