codice:
<script language="JavaScript" type="text/javascript">
window.onload=function(){
document.getElementById('form').onsubmit=function(){
if(document.getElementById('finestra').value=='Nuova'){
var w = window.open('about:blank','Popup_Window','toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0,width=750,height=450,left = 312,top = 234');
this.target = 'Popup_Window';
}
}
}
</script>
<form action="go.htm" method="post" name="form" id="form" >
<select name="finestra" id="finestra">
<option value="Stessa">Stessa Finestra</option>
<option value="Nuova">Nuova Finestra</option>
</select>
<input type="submit" value="Invia">
</form>
Questo fa quello che chiedi, comunque i popup fanno tanto "web 1.0"...