I need to do this navigation, and i'm messing around with the XSLT, can someone help me out? :)

This is the structure:

Website
- level1 navi
-- level2 navi
--- level3 navi
--- level3 navi

        <ul class="undermenu"> 

            <li><a href="#">Level2</a>             

                <ul> 

                    <li><a href="#" class="aktiv">level3</a></li>                     

                    <li><a href="#">Level3</a></li>

                </ul>

            </li> 

        </ul>