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!