Best would be if you modify the bbpress theme a bit.Copy the entire folder “/bbpress/bbp-themes/bbp-twentyten” folder into your themes folder, rename it to something else, and modify your style.css to make it a custom child theme of whatever your current theme is.
Now you can modify as you you wish.
Another way :Copy all files of that folder inside ur theme.
In your theme’s function.php add the following line.
add_theme_support( ‘bbpress’ );
Now you have your theme compatible with ur own bbpress page structure which you can modify as you wish.
Hope that helps