C'est bon, j'ai résolu mon problème. Voici le code pour ceux que ça interesse.
<html xmlns="http://www.w3.org/1999/xhtml" lang="fr" xml:lang="fr"><head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title></title>
<script type="text/javascript">
function showEngineer() {
var fields = document.getElementById("engineer_fields");
if (document.getElementById("Service").value == 'Engineering') {
fields.style.display = "" ;
}
else {
fields.style.display = "none" ;
}
}
window.onload = showEngineer;
</script>
</head><body>
<table height="100%" width="800" border="0" cellpadding="3">
<tr>
<td width="50"> </td>
<td class="champs">Service :</td>
<td>
<select id="Service" name="Service" size="1" onchange="showEngineer();" onkeyup="showEngineer();">
<option>< ------- Choose a service ------- ></option>
<option value="Administration">Administration</option>
<option value="Engineering">Engineering</option>
<option value="IT" >IT</option>
</select>
</td>
</tr>
<tr id="engineer_fields">
<td width="50"> </td>
<td class="champs">Diffusion List : </td>
<td class="champs"><input type="checkbox" name="DevelopmentTeam" value="yes" id="DevelopmentTeam" /> <label for="DevelopmentTeam">Development Team </label> <input type="checkbox" name="Engineering" value="yes" id="Engineering" /><label for="Engineering">Engineering</label></td>
</tr>
</table>
</body></html>
Merci.