And, here's an example like you asked for:
parent.htm:
<html>
<head>
<title>Parent</title>
<script type="text/javascript">
<!--
function openWindow(URL) {
newWin = window.open(URL,'childWin','width=300,height=100');
newWin.focus();
}
// -->
</script>
</head>
<body>
<a href="child.htm" onclick="openWindow('child.htm'); return false" />Link</a>
<form id="form1" action="javascript://">
<input type="text" name="test" value="" />
</form>
</body>
</html>
child.htm:
<html>
<head>
<title>Child.htm</title>
<script type="text/javascript">
<!--
function doSomething() {
if(opener && !opener.closed) {
opener.document.forms[0].test.value = "Yay!";
self.close();
}
}
// -->
</script>
</head>
<body>
<a href="child.htm" onclick="doSomething()" />Yay!</a>
</body>
</html>