Preview: (put your cursor over the image)

Start by opening up dreamweaver and creating a new html file. First thing we need your first image, to get a image from your files you go toolbar > insert > images.

Choose your image and then click it, now go to your right side panel and to behaviors, click the + button and go down and click Swap Image, if you havnt got this option you will need to click Show Events For > IE 6.0 and the option will work.

Now Click Browse... and choose the image you want to swap it with. Now Click Ok.

You Should now have this:

You now know how to use a Swap Image Behavior.