Validar un par de campos...

[America|UNK]

Código HTML:

<form name="manageform">
<select name="mainvals">
<option value="01">Saldos</option>
<option value="22">Cuentas</option>
<option value="25">Salarios</option>
</select>
<input type="text" name="numbox" value="01" />
<input type="submit" />
</form>
 

Código Javascript:

<script type="text/javascript">
var initManage = function(){
    var f = document.manageform, n = f.numbox, m = f.mainvals;
    m.onchange = function(){
        var e = this, v = e.options[e.selectedIndex].value;
        if(v != n.value.substr(0,2)){
            n.value = v;
        }
        n.style.color = '';
    }
    n.onkeyup = function(e){
        var e = this, V = e.value, k = m.options[m.selectedIndex].value;
            e.style.color = V.substr(0,2) != k ? 'red' : '';
    }
    f.onsubmit = function(){
        return (m.options[m.selectedIndex].value == n.value.substr(0,2));
    }
}
initManage() // correr funciones
</script>