How to “plug into” the Media Library (allow users to select images from Media li

I am trying to plug into the WordPress media library to allow users to select images & upload into it for use as the logo in a theme. I think its common but how can I acheive it?

I asked in WordPress StackExchange. So far, I have

// init wordpress media upload stuff ...
if (is_admin() && isset($_GET['page']) && $_GET['page'] == 'elem_opts') {
  wp_enqueue_style('thickbox');
  wp_enqueue_script('media-upload');
  wp_enqueue_script('thickbox');
  wp_register_script('elem_adm_js', get_bloginfo('template_directory') . '/js/admin.js', array('jquery', 'media-upload', 'thickbox'));
  wp_enqueue_script('elem_adm_js');
}

jQuery(document).ready(function($) {
	$('#elem_upload_logo').click(function() {
		tb_show('', 'media-upload.php?type=image&TB_iframe=true');
		return false;
	});

	window.send_to_editor = function (html) {
		imgurl = $('img', html).attr('src');
		$('input[name=elem_opts[h_image]]').val(imgurl);
		tb_remove();
	}
});

It shows the thickbox/media library upload box but there are JS errors …

invalid label
https://elements/wp-admin/media-upload.php?type=image&
Line 49

post_id is not defined
https://elements/wp-admin/load-scripts.php?c=0&load=jquery,utils,swfupload-all,swfupload-handlers,json2&ver=2af6dbb1e89d69a2363895fac893188d
Line 178

JS Errors in FireBug