array in form for ie mac

Hi,

I have a little problem with the internet explorer 5.2 for mac. I have a
checkbox field which name is an array, but then I can't read the field on IE
for MAC. Other browsers don't seem to have problems with it, if I set the
id's of the field the same as the name is. Anybody has a solution?

Code:

<script>
function chklength(field) {
alert(field.length);
}
</script>

<form name="test">
<input type="checkbox" name="testfield[]" id="testfield" value=1>
<input type="checkbox" name="testfield[]" id="testfield" value=2>
<input type="button" onclick="chklength(this.form.testfield)"
</form>

Thanks in advance,
Ben