Hi, funny thing is I currently want to add sidebar for my bbpress forum plugin. It alway shows the wordpress sidebar!
Anyway, to remove sidebar use the fullwidth forum like this: http://www.ytecongcong.com/forums/
1. Clone page.php of your WP themes and rename it to forum.php
2. use BP Tweaks WP plugins to choose forum instead of page as default
3. Open forum.php, remove the php code content php get_sidebar()