ho provato così:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>

<head>
<script type="text/javascript" language="javascript">
function Carattere(SFont){
\\di seguito puoi aggiungere tutti i campi text che vuoi
document.form1.nome.style.fontFamily=SFont
document.form1.cognome.style.fontFamily=SFont
}
</script>
<title>PROVA</title>
</head>
<body>
<form name="form1" method="post" action="">



<input name="nome" type="text" id="nome">
<select name="FontFamily" id="FontFamily" onChange="if(this.value!=0){Carattere(this.options[this.selectedIndex].value)}">
<option value="0" selected>Seleziona</option>
<option value="Arial">Arial</option>
<option value="Verdana">Verdana</option>
</select>
</p>



<input name="cognome" type="text" id="cognome">
</p>
</form>
</body>
</html>

ma mi da errore(previsto oggetto)!