javascript within widget form

Hi,
I am trying to add a widget.
The widgets form should be dynamic.
for example Email filed is shown just if a checkbox is selected.

From some reason i cant get it to work.

Here is the code:

<input id="checkme" type="checkbox" />
<div id="extra">
<label for="email">Email Address:</label>
<input id="email" type="text" />
</div>

and the javascipt:

<script type="text/javascript"> 

	$(document).ready(function(){
		//Hide div w/id extra
	   $("#extra").css("display","none");
		// Add onclick handler to checkbox w/id checkme
	   $("#checkme").click(function(){
		// If checked
		if ($("#checkme").is(":checked"))
		{
			//show the hidden div
			$("#extra").show("fast");
		}
		else
		{
			//otherwise, hide it
			$("#extra").hide("fast");
		}
	  });

		});
	 </script>