Just an update:
It's not necessary to edit the general-template.php file.
Just replace
<?php get_header(); ?>
with
<?php include(TEMPLATEPATH."/whatever-header-file-you-want.php"); ?>
and be sure to save the whatever-header-file-you-want.php file in the theme folder with all the other theme files, including the original header.php file.
You can do the same with sidebar files.
Just replace
<?php get_sidebar(); ?>
with
<?php include(TEMPLATEPATH."/whatever-sidebar-file-you-want.php"); ?>
and be sure to save the whatever-sidebar-file-you-want.php file in the theme folder with all the other theme files, including the original sidebar.php file.