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=utf-8" />
<title>Documento sin título</title>
</head>
<body>
<form id="form1" name="form1" method="post" action="">
<textarea onscroll="document.getElementsByTagName('div')[0].innerHTML=this.scrollTop" name="textarea" rows="3"></textarea>
</form>
<div></div>
</body>
</html>