Now that I can see your site, I see what you mean by "bottom of the page".
You have a bannerbox (bannerbox 6) which you can turn off in admin, and the "Valid XHTML 1.0 Transitional" link which you can eliminate from /includes/templates/your_template/common/tpl_main_page.php.

For the header, I presume you want the body background to show behind the header image. As I said, you can't have a #mainWrapper background tiled and starting below the header; what you can do is give the background-color to #contentMainWrapper instead:

#contentMainWrapper {background-color: #ffffff;}

You will want to do the same with #navSuppWrapper and #siteInfoLegal as well, and #siteInfoIP if you want to leave that showing.

There is no good reason to use an image to make the background white as you were doing.