hi, i think for resolve the probleme look in
http://www.extjs.com/deploy/dev/docs....form.ComboBox
you should define the store data like this:
var ds = new Ext.data.Store({
proxy: new Ext.data.ScriptTagProxy({
url: baseURL + '/extjs.customer_lookup',
nocache: false,
callbackParam: 'p_callback'
}),
reader: new Ext.data.JsonReader({
root: 'rowset',
totalProperty: 'totalRows',
id: 'id'
}, [
{name: 'id', mapping: 'id'},
{name: 'customer', mapping: 'customer'},
{name: 'address', mapping: 'address'},
{name: 'locality', mapping: 'locality'},
{name: 'email', mapping: 'email'}
])
});

var resultTpl = new Ext.XTemplate(
'<tpl for="."><div class="search-item">',
'<h3>{customer} {credit_limit}</h3>',
'{address}<br />',
'{locality}<br />',
'{email}',
'</div></tpl>'
);

var search = new Ext.form.ComboBox({
store: ds,
displayField:'customer',
valueField:'id',
typeAhead: false,
itemSelector: 'div.search-item',
transform: el,
emptyText:'Customer search (2+ chars)...',
loadingText: 'Searching...',
width: el.getWidth(),
pageSize:10,
// hideTrigger:true,
tpl: resultTpl,
triggerClass:'x-form-search-trigger',
triggerAction:'all',
minChars:2,
queryParam:'p_query'
});

the display value and the value field will figured in the defenition of store data...
i hope that help you
regard sihem