it's pretty hard to get people to click ads that are pretty apperent as that. Which is mainly why google ads uses text links and integrated graphics. i would check to see if you could use you're own graphic and go from there.
The text on a banner is what really draws me in, the image is the flair and the text is the seller. This in mind you may try 3 different banners with different text and see which one produces the most clicks.