You have to create the invisible button yourself.
1) Go to Insert, then New Symbol
2) Select Button, and give it a name
3) The button creation window opens
4) The window will have 4 frames already labeled
Up Over Down Hit
5) These represent the states of the button with respect to the mouse.
6) oldnewbie is telling you to create a keyframe in the "HIT" state of the button. To create a keyframe right click your mouse while it is over the "HIT" Frame, and select "Insert Keyframe".
7) Now you need to draw a rectangle on the screen the size of your banner. You can make it any color you want.
8) After drawing a rectangle select it with your mouse, then go to the "MIXER" pallete which will be right next to the "SWATCHES" pallette.
9) Select "ALPHA" from the mixer pallette, and give it an alpha value of "0".
10) Now go back to your main movie and open the library.
11) Drag out the button which you just created and put it over your banner.
12) Now right click the invisible button and select "ACTIONS", and give it the actions oldnewbie showed you.