Prova questo

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
var myArr = new Array();
function assegnaArray(aForm) {
 a          = 0;
 var tmpArr = new Array();
 nbFigli    = aForm.children.length;
 for (i=0;i<nbFigli;i++) {
  curFiglio = aForm.children(i);
	if (curFiglio.tagName == 'INPUT' && curFiglio.type == 'text') {
	 tmpArr[a++] = curFiglio.value;
	} //  if (curFiglio.tagName == 'INPUT' && curFiglio.type == 'text')
 } // for (i=0;i<nbFigli;i++) 
 return tmpArr;
} // function assegnaArray(aForm)

function ass() {
 myArr = assegnaArray(document.getElementById('myform'));
 alert(myArr);
} // function ass()
//-->
</script>

</head>
<body>
<form action="" method="post" id="myform">
 A<input type="text" id="c[0]">

 B<input type="text" id="c[1]">

 C<input type="text" id="c[2]">

 D<input type="text" id="c[3]">

 E<input type="text" id="c[4]">

</form>
<input type="button" value="Assegna" onclick="ass()">
</body>
</html>