[bes]

вот тебе два варианта, жду пива

<script src="http://code.jquery.com/jquery-1.8.3.min.js"></script>
<style>
.backing {
	position: fixed;
	width: 100%;
	height: 100%;
	z-index: 100;
	background-color: green;
	opacity: 0.2;
	display: none;
}
.form {
	position: relative;
	z-index: 101;
	display: none;
	background-color: yellow;
}
</style>
<div class="backing"></div>
<button class="but">show/hide form</button>
<a href="#">link</a>
<button onclick="alert('click')">click</button>
<form class="form">
	<input/><br/>
	<input/><br/>
	<input type="submit"/>
</form>
<script>
jQuery(function ($) {
	$(".but").on("click", function () {
		$(".form").toggle();
		$(".backing").show();
	});
	$(".backing").on("click", function (e) {
		$(".form").toggle();
		$(this).hide();
		var elem = document.elementFromPoint(e.clientX, e.clientY);
		if (elem.className != "but") {
			elem.click();
		}
	});
});
</script>

<script src="http://code.jquery.com/jquery-1.8.3.min.js"></script>
<style>
.form {
	position: relative;
	z-index: 101;
	display: none;
	background-color: yellow;
}
</style>
<div class="backing"></div>
<button class="but">show/hide form</button>
<a href="#">link</a>
<button onclick="alert('click')">click</button>
<form class="form"  onclick="event.stopPropagation()">
	<input/><br/>
	<input/><br/>
	<input type="submit"/>
</form>
<script>
jQuery(function ($) {
	$(document).on("click", function () {
		$(".form").hide();
	});
	$(".but").on("click", function (e) {
		$(".form").toggle();
		e.stopPropagation();
	});
});
</script>