i posted a demo here awhile ago.
Code:
<SCRIPT type="text/javascript">
var bResult;
function fC(){
event.returnValue = false;
var cstr=document.selection.createRange().text;
bResult = window.clipboardData.setData("Text",cstr + " Courtesy of <a href='"+document.location.href+"'>"+document.title+"</a>");
}
</script>
place that in head.. then add the even handler oncopy="fC();" to the container holding your text..
such as <div id=mytext oncopy="fC();"> some words i want to protect </div>