Rails - Apr 2006 - doing synchronous JSON on rails

So I have found how to generate json in a rails app in the wiki 
(http://wiki.rubyonrails.com/rails/pages/HowtoGenerateJSON), what I have 
yet to figure out is how to make a synchronous call via json to rails so 
that I can block while fetching the information from a user request.

context:
I have used JSON on top of java in the past, and in order to make 
synchronous calls I had to do the following:
1) include json.js

	<script type="text/javascript" src="jsonrpc.js">
	<script type="text/javascript" src="myapp.js">

2) add the json object to the page:

	<jsp:useBean id="JSONRPCBridge" scope="session
class="com.metaparadigm.jsonrpc.JSONRPCBridge" />

3) in the jsp, register a json object as an object that can be called 
from the javascript of the page

	<% JSONRPCBridge.registerObject("myTestObject", aTestObject);
%>

4) Register the JSON Servlet
5)  Then call the function either async:

	jsonrpc.myTestObject.myFunction(myCallBack, "hello");

or sync:

        var result = jsonrpc.myTestObject.myFunction("hello");
        alert(result);

 
I would like to know how I would go about getting to #5 in rails and 
http://wiki.rubyonrails.com/rails/pages/HowtoGenerateJSON really only 
explains the actual writing out of the JSON object.

Thanks,
Devon Jones