Oh, also, this would not allow each member to change thier background just you. However, there are a couple of image plug ins that you can take apart and Frankenstein them to make that. I have done this several times with backgrounds and header images for category pages.
You can add your own with css. The big problem with it though will come if your not familiar with how they are coded and the template system. The profile pages dont really work like static pages so its a bit different. You can use firefox with fire bug to help you track down the right places to edit thought.