var duringAjaxRequest = false

function SendAjaxRequest(url, sender)
{
    if (!duringAjaxRequest)
    {
        duringAjaxRequest = true;
        
        new Ajax.Updater(
            sender, 
            url, 
            {
                asynchronous:true, 
                evalScripts:true, 
                onComplete:function(request){RequestCompleted()}                    
            });
    }
}

function RequestCompleted()
{
    duringAjaxRequest = false;
}