Sending A Value To Parent Window

On the main window, you click a link and it pops up another window, where you can do some stuff, and ultimatly you get a variable that has some value to it. Now, when the user clicks "All Done", I want that variable value to be become the value of a hidden input "attachments" back in the main window.

Code:

<script language="javascript">
function sendUploads() {
var newValue = &#392;'
parent.document.addform.attachments.value = newValue;
}
</script>

The main window's form is called "addform" and the hidden input is called "attachments".