VAs..
<script type="text/javascript">
function Deshabilitar(){
Forma = document.getElementById("MiForma");
Elementos = Forma.getElementsByTagName("input");
alert('Se encontraron '+Elementos.length+' Elementos que se van a deshabilitar');
for (i=0;i<Elementos.length;i++){
Elementos[i].disabled = true;
}
}
</script>
<form id="MiForma" method="post" action="">
<input type="text" name="textfield">
<input type="text" name="textfield2">
<input type="text" name="textfield3">
<input type="text" name="textfield4">
<a href="javascript
: Deshabilitar();">Deshabilitar</a><br>
<input type="text" name="textfield5">
</form>