Linked dropdown List

Hello, I need help for a contact form for a car site. I need 2 linked dropdown lists. When you choose in the first list a value.. in the second list must appear a new menu that in linked tot the first chose). The second menu contains the model of the car. I want to help me just for the first selection from the brands menu(first menu).

Sorry for my bad english .

 $marca = stripslashes ($_POST['marca']); //Marca masinii
 
 
 
 <!-- Marca -->
                    <p>
                    <label for="marca"><strong><span class="blue">*</span>Marcă : </strong></label>
                    <select name="marca" id="q1" >
         <option >Vă rugăm selectaţi</option>
     <option >Alfa Romeo</option>
     <option >Audi</option>
     <option >BMW</option>
     <option >Chrysler</option>
     <option >Citroen</option>
     <option >Dacia</option>
     <option >Daewoo</option>
     <option >Dodge</option>
     <option >Fiat</option>
     <option >Ford</option>
     <option >Hyundai</option>
     <option >Isuzu</option>
     <option >Jeep</option>
     <option >Land Rover</option>
     <option >Lexus</option>
     <option >Mazda</option>
     <option >Mercedes-Benz</option>
     <option >Mitsubishi</option>
     <option >Nissan</option>
     <option >Opel</option>
     <option >Peugeot</option>
     <option >Renault</option>
     <option >Saab</option>
     <option >Seat</option>
     <option >Skoda</option>
     <option >Subaru</option>
     <option >Suzuki</option>
     <option >Toyota</option>
     <option >Volvo</option>
     <option >Volkswagen</option>
     <option >Altceva</option>
                    </select>
         </p>
 
 

Code (markup):