Ajax cross domain calls with IE7, 8 and 9

I need to make calls using Ajax to PHP files that query a database . The PHPs are on a different domain to the HTML files, therefore my current code won’t work in IE,7, 8 and 9. Here are examples of the calls to the phps on the other domain.

$.post('http://other-domain.com/promo_subscribe.php', subscribeData, function(data){


 $.get('http://other-domain.com/misc/promo_getstate.php', {
                crossDomain : true,
                email: emailaddress,
                country: 'DE',
                lang: lang,
                source: 'Spring_dly'
            }, function (test) {


What is the best option for me? Does it require a back end change ?