jQuery Grid Plugin - jqGrid

I'd like to add a dialog to the add/edit function of a subgrid that enables a part number lookup.  Seems straightforward but I'm getting ".dialog is not a function" errors when I place $(function() {$( "#lookupForm" ).dialog();}); anywhere in the index or js files.  Is there a compatibility issue with jQuery 1.5.2 and Grid 4.0.0?

Code:

subGridRowExpanded: function(subgrid_id, row_id) {

subgrid_table_id = subgrid_id+"_t";

pager_id = "p_"+subgrid_table_id;

$("#"+subgrid_id).html("<table id='"+subgrid_table_id+"' class='scroll'></table><div id='"+pager_id+"' class='scroll'></div>");

r = $("#partitions").getRowData(row_id),

h_id = r.h_id,

$("#"+subgrid_table_id).jqGrid({

url:"getBOM.php?h_id="+h_id,

datatype: "json",

colNames: ['Partition ID','Part #','Software','Unit List Price'],

colModel: [

{name:"partition_id", hidden: true, editable: false},

{name:"part_num", width: 100, editable: true}, //would like to include a button to press here in order to "open" the modal dialog

{name:"prod_desc", width: 400, editable: false},

{name:"price", width: 100, editable: false}

],

viewrecords: true,

editurl: 'addBOM.php',

height: 100,

pager: pager_id,

rowNum: 10,

sortname: 'prod_desc',

sortorder: 'asc',

sortable: true

});