If You are talking about:
http://twitter.github.io/bootstrap/You could add those files into template folder, then edit:
/templates/gk_twn2/layouts/blocks/header.php and add lines:
$this->API->addCSS($this->API->URLtemplate() . '/css/FILENAME.css');
to load css and
$this->API->addJS($this->API->URLtemplate() . '/js/FILENAME.js');
to load js.
But be aware, as this bootstrap is an entire "framework" and its styling might collide with ours, making templates broken.