I'm not sure what you mean by "don't work," so I'm going to go with just a few suggestions instead.
I'm not sure about Safari, but Internet Explorer will cache the results, causing a hiccup in your expectations. You can avoid this by appending a constantly-changing value onto the query-string.
function loadContent(id, start) {
var t = new Date;
$.get("cast_member.php", {'_type':id,'start':start,'t':t.getTime()}, function(result) {
$("#ContentRightBlockTest").html(result);
});
}
Additionally, it's advised to wait until the DOM has completely finished loading before firing off any requests. As such, jQuery code is best placed within the ready() event of the document. Below is a short-hand representation of this containing your function call.
$(function(){
// Fire loadContent() once DOM is loaded
loadContent('cast', 4);
});