Hi,

Here's a quick example. Try selecting some of the text in the textarea it should (hopefully ) alert the bit of the text you selected

Code:
<html>
<head>
<script type="text/javascript">

onload = function() {
    document.getElementById('txt').onmouseup = function() {
        if (document.selection) { // for IE
            alert(document.selection.createRange().text);
        } else if (typeof this.selectionStart != 'undefined') { // for FF, Opera etc...
            alert(this.value.substring(this.selectionStart, this.selectionEnd));
        } else {
            alert('Could not find selection');
        }
    };
};

</script>
</head>
<body>
<textarea id="txt" rows="10" cols="50">hello! please select me</textarea>
</body>
</html>
Tested in IE 6, FF 2 and Opera 9.