SWAP IMAGES ON HOVER

SWAP IMAGES ON HOVER

Hi, I have a dropdown menu with a list (made out of divs) on the left and images on the right. I want the images to change depending on which list item you hover. here is my html code

Help very much appreciated!

<div class="dropdown">
                        <!---Flecha--->
                        <div class="arrow">                           
                        </div> 
                        <!---Menu--->
                        <div class="parte_baja">                 
                            <div class="drop_izq">                              
                                <div class="drop_titulo"><a href="">Summer 2010</a></div>
                                <div class="drop_titulo"><a href="">Navidad 2011</a></div>
                                <div class="drop_titulo"><a href="">Aqui Decide</a></div>
                                <div class="drop_titulo"><a href="">Usted</a></div>
                                <div class="drop_titulo"><a href="">Que poner</a></div>                               
                            </div>
                            <div class="drop_der">
                                   <div class="der_1" style="vertical-align:top">
                                        <a href="#"><img src="images/falsas/modelo_1.jpg" height="180" /></a>
                                </div>
                                <div class="der_2" style="vertical-align:top">
                                        <a href="#"><img src="images/falsas/modelo_2.jpg" height="180" /></a>
                                </div>             
                            </div>                         
                        </div>
                    </div>