Passing HTML form and hidden variables from html to flash

Hi

I need some help passing a html code to flash code. Maybe you guys can set some light on the subject.

<html>

<script>
function Dimensiones()
{

document.getElementById("tamx").value= document.getElementsByTagName('body')[0].clientHeight;                  
document.getElementById("tamy").value= document.getElementsByTagName('body')[0].clientWidth;                       

 }

</script>
<body ONLOAD=“Dimensiones();” ONRESIZE=“Dimensiones();”>
<form method=“Post”
action=“http://Validation link.asp”>
<input type =“hidden” name=“tamx”>
<input type =“hidden” name=“tamy”>
<input type =“hidden” name=“url_return” value =“http://Link.asp”>
<input type =“hidden” name=“url_ot” value = “http://Validation link.asp”>
Nombre <input type=“text” name=“UserName” value="" size=“20”>
Password <input type=“password” name=“UserPass” size=“20”>
<INPUT type=“submit” value=“Enviar”>
</form>
</body>
</html>

I’m having a real hard time passing the function Dimensiones() and dealing with the hidden variables. Can you guys help me with this? Thanks