Here's your problem:
Code:
<a href="http://halosource.info"><img id="topbanner"
width="100%"
height="40%"
src="top.jpg"
alt="Halo Source - The Halo Information Database" /></a>
I'm not sure you'll get your desired result by scaling a jpeg this way. It's best practice to specify your image dimensions in pixels. I see what you're trying to do, but trust me there's a better way -- sorry, no time to make an example, but make full-height side images, take the middle section and split it in half lengthwise. Align the top half (plus left side image) to the left-top, and the bottom half (plus right side image) to the right-bottom.