Wordpress is great as a CMS and one way to make sections of a custom template editable is to use seperate posts for each section of the page.
To do this use the following code for the section you want to make editable:
<?PHP
$queried_post = get_post('XX');
echo wpautop($queried_post->post_content);
?>
The number XX is the ID of the post. You need to create a post and make a note of the post ID and replace XX with this.
You also need to make the post Private so that it does not show up on any blog pages.