It's always a good idea to validate your code. Your page has it's share of errors and warnings. http://validator.w3.org/
but 600kb for a large background is not THAT bad.
An option to reduce size the image size would be to use two images....one, a top image of just the landscape down to the bottom of the grass, and a second, a tall, thin image of the just the cream colored section of the photo.
Then set up a <div> that will hold two other <divs>, a top part 1660 x 800 or so to hold the landscape image as background. And then a bottom <div>, 1600 x 1400 or so uses the tall thin cream colored image and justs repeats it.
It's a little extra work but it would reduce the file size of that very large background image, the bottom 2/3 of which contains no detail and could just as easily be a repeat pattern rather than part of the larger image.
Eye for Video www.cidigitalmedia.com