non funge

codice della pagina principale:
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 
<html> 
<head> 
<title>Prova</title> 

<script type="text/javascript">
function ciao(){
document.getElementById("testo").value=document.getElementsByName("borse").value;
}
</script>
</head> 

<body> 
<script type="text/javascript">
window.open("borse.htm","borse");
</script>
premi
<textarea name="testo" cols="40" rows="15" id="testo"></textarea>
</body> 
</html>
risultato: undefined --- ancora