+1 on the overkill. Including json2.js is the way to do this.
AJAX is not in any way intrinsically linked to the use of JSON, which is just a generic data interchange format that happens to be often used in conjunction with AJAX. On the other hand, GET and POST params ''are'' linked to AJAX requests, in that there already exists a well-defined standard for sending additional data to a web server when an HTTP request is made.
While JSON would be my recommended approach for large objects (including a json2.js shim for older browsers), you can use the already-built-in
jQuery.param method to convert a data object into GET or POST params for any AJAX request, which most web servers are configured to handle.
In fact, this method is automatically used by jQuery to serialize params when an object is passed as the "data" parameter in a jQuery AJAX call.