Got it all working (with my version of the checkbox) with this

function mychkclick(rowid, colid) {

val = $(“#list4”).getCell(rowid, colid);

newValue = “1”;

if (val == “1”) newValue = “2”;

$(“#list4”).setCell(rowid, colid, newValue);

val = $(“#list4”).getCell(rowid, colid);

}

jQuery.extend($.fn.fmatter , {

mycheckbox : function(cellvalue, options, rowobject) {

var checked = cellvalue == '2' ? “checked='checked' ” : “”;

var disabled = cellvalue == '0' ? “disabled='disabled' ” : “”;

rtn = “”;

return rtn;

}

});

jQuery.extend($.fn.fmatter.mycheckbox , {

unformat : function(cellvalue, options, cellobject) {

var checked = $(cellobject).html().indexOf(“checked”,0) != -1 ? “2” : “1”;

return checked;

}

});

var mydata = [

{id:”1″,name:”test”,checkbox:1},

{id:”2″,name:”test2″,checkbox:0},

];

jQuery(“#list4”).jqGrid({

datatype: “local”,

data: mydata,

height: 250,

colNames:['id','name','checkbox'],

colModel:[

{name:'id',index:'id', width:60, sorttype:”int”},

{name:'name',index:'name', width:100},

{name:'checkbox',index:'checkbox', width:80, align:”right”,sorttype:”float”,editable:true,edittype:'select',formatter:'mycheckbox',formatoptions:{disabled:false}, },

],

multiselect: true,

caption: “Demo”

});