How I did it... Please back up everything before starting.
You need to find a theme close to your WP to make it easier.
1. BBPress side,I renamed the style.css to styleold.css
2. Copied over the WPress style.css over to BBpress
3. Open both files at the same time. You want to copy over some of the codes from styleold.css to style.css. You might need to play with it. Do not copy "body".
4. Open both header.php. On the BBpress header copy over from WP header everything after <body> tag. Replacing whatever is there.
5. Open both footer.php. This one is a little tricky.
You can just copy over the whole thing and make sure you have <?php do_action('bb_foot', ''); ?> in the file. You will lose the designers info though OR You need to see on WP side if there is any closing tags. bring that over and delete any closing tags on the BBPress side.
6. Sidebars: depending where the <?php get_sidebar(); ?> tag. For example my <?php get_sidebar(); ?> tag is IN the footer.php Others the <?php get_sidebar(); ?> is in the other php files right before the get_footer tag or after get header tag.
that's it.
make sure in your bb-config.php
there is
$bb->WP_BB = true;
if (file_exists('../wp-blog-header.php'))
require_once('../wp-blog-header.php');
else
if (file_exists('../../wp-blog-header.php'))
require_once('../../wp-blog-header.php');
after <?php tag.
Goodluck.