When using a dialog box, how do I target it for content swaping?

When using a dialog box, how do I target it for content swaping?

I'm starting with: 
  1. function run_modal(catagory, item) {
    //    alert(catagory +'*'+ item);



    //modal code for output
        $( "#modal" ).dialog({
            //modal content in here
            title:"this is only a test",//title of modal box
            width: 300,
            height: 300,
            modal: false,
            ui-dialog-content:"text",

        });

    }

I intend to be able to use the ajax (think success innerhtml) feature to do a page request on the back end  to hot-swap the forms, as it could take forever to load the data.  What do I need to do in order to target the lower part of the dialogue box for hot swapping capability with jquery?

Is this even possible yet with the dialogue box?