function open_chat() {
    if (screen.width <= 800) {
	applet_size = 1
    }
 else {
	applet_size = 2
    }
	if (applet_size == 1) {
	    window_app = 'toolbar=no,location=no,directories=no,status=yes,menubar=no,scrollbars=no,resizable=yes,width=800,height=550';
	} else {
	    window_app = 'toolbar=no,location=no,directories=no,status=yes,menubar=no,scrollbars=no,resizable=yes,width=920,height=620';
	}
    query='id=1292' + '&' + 'chatnow=' + document.chat.chatnow.value  + '&' + 'nickname=' + document.chat.nickname.value  + '&' + 'age=' + document.chat.age.value  + '&' + 'sexe=' + document.chat.sexe.value  + '&' + 'ville=' + document.chat.ville.value  + '&' + 'applet_size=' + applet_size;
    window.open('http://www.chat-fr.org/applet_partenaires.php?' + query, 'chat', window_app);
    return;	
}