BuddyPress.org

Again, this isn’t very clear.
Please outline your steps.

Let’s say your external bbPress install is located under /bbpress/.
Your custom template would reside in /bbpress/my-templates/YOURNEWTHEME/.

In this case, you’d want to put “bbbp-default” under /bbpress/my-templates/.
Then you go to /bbpress/bb-admin/ and activate the bbPress theme.

It’d also help to read the theme’s instructions. According to the theme author, you also need to add deep integration.

What is deep integration? Read the following article and read the section on deep integration:
http://wpwebhost.com/make-bbpress-theme-match-with-wordpress-by-deep-integration/