BuddyPress.org

Glad you got the extra bit, jeffreeeeey, but you might want to clean up that code a bit, to make sure you close the HTML tags correctly:

<?php if ( !is_user_logged_in() ) { ?><li <?php if ( bp_is_page( BP_REGISTER_SLUG ) ) : ?> class="selected"<?php endif; ?>><a href="register">Sign up!</a></li><?php } ?>

What exactly do you want the else clause to do? Do you want different button to show up when the user is logged in?