Very odd. I'm baffled. It's symmetrical when I re-size to 800x600 - and in Opera and IE too...
Everything looks to be in order in the code, but I can't check out whether any changes to the CSS make any difference because it's showing up fine as it is for me. The only thing I could think of that could possibly influence it would be the 100% height you've got on the html and body, but as your images are the same width and height, if they were going to get stretched or squished, it'd be in the same proportions, so it can't be that.
The only thing I have noticed is that when I highlighted the block level elements using the FF web dev toolbar, the right hand image div is 300px while the image itself is 250px, whereas the left hand image div and image are both 250px. Does it make any difference if you make that right hand image div 250px wide?
If not, I'm stumped.
