Fijate si te sirve:
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>
<style>
a.pp{ color:#F00}
</style>
</head>
<body>
<a href="#" class="pp" onclick="alert(this.className)">enlace a</a> | <a onclick="if(!this.className.length){alert('sin clase');this.className='pp';}" href="#">enlace b
</a>
</body>
</html>