inArray is case sensitive
HTML
<ul>
<li><li><li><li><li>
</ul>
JavaScript
var arr = ["Peter","pete"];
var v = "Peter".toLowerCase();
$("li:eq(0)").text($.inArray(v, arr));
$("li:eq(1)").text($.inArray(v, arr));
$("li:eq(2)").text($.inArray(v, arr));
$("li:eq(3)").text($.inArray(v, arr));