Bad title. Very cool site. Over 300 free backgrounds for your blog. I just did it and it took seconds. The basic, center layout remained the same, so I didn't need to reconstruct the page. Each background comes with a bit of code, which you copy and paste into the HTML/Java Script screen. It's wicked easy. The following has been copied directly from their site.
1. Sign in to Blogger. This will take you to your Dashboard.
2 Under the blog you wish to change the background for, click on Layout.
3. You are now in the 'Add and Arrange Page Elements' screen. Click 'Add a Gadget'.
5. Next to that, click on the (+) sign.
7. Click 'Save'.
You guys are gonna love this. They'll even design a custom banner to match your background for $30. Wicked talented chicks.