Try .getJSON().
var url = "http://pinterestapi.co.uk/"+pinterestUsername+"/pins";
$.getJSON(url, function(data) {
alert(data);
});
Ok, lets try something different...
Assuming you are the user "jwmoz".
var user = "jwmoz";
var url = "http://pinterestapi.co.uk/"+user+"/pins";
$.get(url,
function(data) {
alert(data)
}, "jsonp");
Check out this page jQuery AJAX cross domain, this should give you a rough idea and several userful links to solve your problem.
Ps- sorry for misunderstanding your question first time around! Best of luck!!
Dom