http://learn.javascript.ru/play/rfer6b
<!DOCTYPE HTML>
<html>
<head> </head>
<body>
<iframe name="fr1" height="200px" width="100%"></iframe>
<iframe name="fr2" height="200px" width="100%"></iframe>
<form action="http://javascript.ru/" id="url" method="get" target="fr1, fr2">
<input type="submit" value="Send">
</form>
<script>
document.getElementById('url').onsubmit = function() {
var tmp = this.target,
target = tmp.split(/, ?/);
for(var i in target) {
this.target = target[i];
this.submit();
}
this.target = tmp;
return false;
}
</script>
</body>
</html>