How can I use Pages in drupal 7?
The Context module would help here. It allows make 'sections' within your site based on selection rules like the path, views or menus chosen etc. Using Context you can apply a CSS class to the body based on the current section and then make the background image change based on that.

Context also allows you to use alternative layouts and you to re-order blocks as needed, and there are many add-on modules for it to extend its abilities further.