Using the theme options to change background

how do I add some options to a theme?
I would like to add support, in my thmes, for dinamically changing the page background.
I don’t even know how to start.

I think I can break down this issue in two questions:

1. how do I add a “theme options page”
2. how do I create a function that prints the link to an uploaded
   image, so I can hardcode the css in my header.php

thank you!

For theme Settings see Chip Bennett’s tutorial, also WordPress supports custom background, you can add support to your theme with add_custom_background, see reference for more information.