For this you need to add another Sidebar to your theme even though it's not actually in the sidebar.
In the latest Twenty Ten theme that comes with WP they have an example.
In the theme there is a functions.php file that has a function to register a footer sidebar:
So this causes the new sidebar to show up in the Admin area of your blog so you can drag and drop widgets to it. Assuming you selected the theme using this code.
// Area 3, located in the footer. Empty by default.
'name' => __( 'First Footer Widget Area', 'twentyten' ),
'id' => 'first-footer-widget-area',
'description' => __( 'The first footer widget area', 'twentyten' ),
'before_widget' => '<li id="%1$s" class="widget-container %2$s">',
'after_widget' => '</li>',
'before_title' => '<h3 class="widget-title">',
'after_title' => '</h3>',
But now you need to add the place-holder code to your theme.
In the twenty ten theme, I see this code in the footer.php code:
But I don't see how this code relates 'footer' to the first block of code.
get_sidebar( 'footer' );
I haven't done this myself but I hope this gets you started in unraveling one of the many mysteries of WordPress.
The help page is at:
Widgets API � WordPress Codex