First save the background image file and upload it to your storage site like Photobucket or your own Site.
To apply this background:
1. Log onto your blog.
2. Click on your 'Design' tab or 'Layout' tab.
3. Click 'Add a Gadget'.
4. Click on the (+) sign next to 'HTML/JavaScript'.
5. Paste the entire code in that space.
6. Click 'Save'
Here is the Code for this background:
<style type="text/css">body {background-image:
url("http://yoursite/aaXmasBg001.jpg ");
background-position: center; background-repeat: no-repeat; background-attachment: fixed;
}</style>
ENJOY!