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>
<script type="text/javascript">
function loquesea(){
alert('acá hacés algo');
}
function ver(e,callback){
if(e && e.stopPropagation)
e.stopPropagation();
else if(window.event)
window.event.cancelBubble=true;
var t=e.keyCode || e.wich;
if(t==13){
callback();
return false;
}
return true;
}
</script>
</head>
<body>
<form action="" method="get"><textarea onkeydown="ver(event,loquesea)" name="" cols="60" rows="5"></textarea></form>
</body>
</html>