Open up twentyten theme's header.php, find and replace this:

<?php wp_nav_menu( array( 'container_class' => 'menu-header', 'theme_location' => 'primary' ) ); ?>

with

			<ul id="nav">
<?php switch_to_blog(1); ?>
				<li<?php if ( bp_is_front_page() ) : ?> class="selected"<?php endif; ?>>
					<a href="<?php echo site_url() ?>" title="<?php _e( 'Home', 'buddypress' ) ?>"><?php _e( 'Home', 'buddypress' ) ?></a>
				</li>
				<?php if ( 'activity' != bp_dtheme_page_on_front() && bp_is_active( 'activity' ) ) : ?>
					<li<?php if ( bp_is_page( BP_ACTIVITY_SLUG ) ) : ?> class="selected"<?php endif; ?>>
						<a href="<?php echo site_url() ?>/<?php echo BP_ACTIVITY_SLUG ?>/" title="<?php _e( 'Activity', 'buddypress' ) ?>"><?php _e( 'Activity', 'buddypress' ) ?></a>
					</li>
				<?php endif; ?>
				<li<?php if ( bp_is_page( BP_MEMBERS_SLUG ) || bp_is_member() ) : ?> class="selected"<?php endif; ?>>
					<a href="<?php echo site_url() ?>/<?php echo BP_MEMBERS_SLUG ?>/" title="<?php _e( 'Members', 'buddypress' ) ?>"><?php _e( 'Members', 'buddypress' ) ?></a>
				</li>
				<?php if ( bp_is_active( 'groups' ) ) : ?>
					<li<?php if ( bp_is_page( BP_GROUPS_SLUG ) || bp_is_group() ) : ?> class="selected"<?php endif; ?>>
						<a href="<?php echo site_url() ?>/<?php echo BP_GROUPS_SLUG ?>/" title="<?php _e( 'Groups', 'buddypress' ) ?>"><?php _e( 'Groups', 'buddypress' ) ?></a>
					</li>
					<?php if ( bp_is_active( 'forums' ) && ( function_exists( 'bp_forums_is_installed_correctly' ) && !(int) bp_get_option( 'bp-disable-forum-directory' ) ) && bp_forums_is_installed_correctly() ) : ?>
						<li<?php if ( bp_is_page( BP_FORUMS_SLUG ) ) : ?> class="selected"<?php endif; ?>>
							<a href="<?php echo site_url() ?>/<?php echo BP_FORUMS_SLUG ?>/" title="<?php _e( 'Forums', 'buddypress' ) ?>"><?php _e( 'Forums', 'buddypress' ) ?></a>
						</li>
					<?php endif; ?>
				<?php endif; ?>
				<?php if ( bp_is_active( 'blogs' ) && bp_core_is_multisite() ) : ?>
					<li<?php if ( bp_is_page( BP_BLOGS_SLUG ) ) : ?> class="selected"<?php endif; ?>>
						<a href="<?php echo site_url() ?>/<?php echo BP_BLOGS_SLUG ?>/" title="<?php _e( 'Blogs', 'buddypress' ) ?>"><?php _e( 'Blogs', 'buddypress' ) ?></a>
					</li>
				<?php endif; ?>
				<?php wp_list_pages( 'title_li=&depth=1&exclude=' . bp_dtheme_page_on_front() ); ?>
				<?php do_action( 'bp_nav_items' ); ?>
<?php restore_current_blog(); ?>
			</ul><!-- #nav -->