BuddyPress.org

In your test user blog, is it just in the plugins list and needs to be activated or is it already active and shows the plugin admin menu?

You can disable Plugins in the /plugins/ dir to show up for your users under Site Options, at the bottom.

You can manually activate plugins for user blogs later.

There is a plugin (Plugin Commander) that allows you to control all the plugins in your /plugins/ dir.