Réponse acceptée !
<!- By sl4k -->
<!- Email: pisoka000@yahoo.com -->
<html>
<head><title></title>
<script>
function choix(id){
champ1.style.display = (id.options[id.selectedIndex].value=="valeur1") ? 'block' : 'none';
champ2.style.display = (id.options[id.selectedIndex].value=="valeur2") ? 'block' : 'none';
champ3.style.display = (id.options[id.selectedIndex].value=="valeur3") ? 'block' : 'none';
}
</script>
</head>
<body>
<select onChange="choix(this);">
<option></option>
<option value="valeur1">valeur1</option>
<option value="valeur2">valeur2</option>
<option value="valeur3">valeur3</option>
</select>
<div id="champ1" style="display:none;"> La 1ere zone : <input type="text" value="champ1"></div>
<div id="champ2" style="display:none;"> La 2eme zone : <input type="text" value="champ2"></div>
<div id="champ3" style="display:none;"> La 3eme zone : <input type="text" value="champ3"></div>
</body>
</html>