Otra manera:
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title></title>
<script>
function noSel() {
this.onselectstart = function() {
return false;
};
this.unselectable = "on";
this.style.MozUserSelect = "none";
this.style.cursor = "default";
}
window.onload=function(){
noSel.call(document.getElementById('ejemplo'));
}
</script>
</head>
<body>
<div id="ejemplo">Texto no seleccionable. </div>
<div>Texto seleccionable. </div>
</body>
</html>