I wrote something similar to this. Well, simply put all you need to do
is listen for mouse clicks on the panel and connect them using Graphics
methods after the fourth click. Then repaint the panel.

(But obviously the four clicks might not form a rectangle. They might
form any old polygon. If you strictly want a rectangle you might have
to check the validity of the points.)

You will need to have a data model to store everything. So you need a
rectangle class and a Collection in which you can add/remove
rectangles.  After the fourth click, create a rectangle object and
store it in the collection. Then when you want to save the diagram you
can loop through the collection and generate the appropriate XML for
each rectangle.

Your XML for a diagram with rectangles might look like:

<diagram>
<rectangle x="10" y="10" width="100" height="50" />
<rectangle x="10" y="100" width="50" height="100" />
</diagram>

Hope this helps,

--
Fahd Shariff
http://www.fahdshariff.cjb.net
"Let the code do the talking... "