Download da versão 0.95 jquery.include.js 1.2 KB (gzip)
Aplicando:

Demo Dialog (dialog ui)

Demo FancyBox

Segue o plugin descompactado em versão de testes:

; jQuery.include || (function($) {
	$.include = function(url,callback,options){
		var options = $.extend({ target: null, elements: null, eventType: '', count: 0}, options);
		if(typeof url=='object') {
			options.count = 1;
			if ($.isFunction(callback))
				$.include.call.push({success:callback, target:options.target, elements:options.elements, eventType:options.eventType});
			if (typeof url.length != "undefined") {
				$.include.count.i+=url.length;
				while (url.length) {
					$.include(url.shift()+'', null, options);
				}
			} else {
				$.each(url, function(){$.include.count.i++});
				$.each(url, function(index, element) {
					$.include(index, element, options);
				});
			}
		} else {
			if($.inArray(url, $.include.past)<0){
				$.include.past.push(url);
				if (/.js$/.test(url)) {
					$.ajax({
						type: 'get',
						url: url+'',
						dataType: 'script',
						cache: true,
						success: function() { $.include.callback(callback, this, $(this), options.count) }
					});
				} else if (/.css$/.test(url)) {
					var link = document.createElement('link');
					$(link)
						.attr({'href':url+'','rel':'stylesheet','type':'text/css'})
						.ready(function() { $.include.callback(callback, this, $(this), options.count) });
					document.body.appendChild(link);
				} else {
					var img = $.include.img.length;
					$.include.img.push({ img : $('').attr('src',url+'').bind('load readystatechange', function() { $.include.callback(callback, this, $(this), options.count) }) });
				}
			} else {
				callback(callback, options.target, options.elements, options.count);
			}
		}
	};
	$.extend(
		$.include,{
			past:[],
			count:{'i':0,'o':0},
			call:[],
			callback: function (callback, target, elements, count) {
				$.include.count.o += count;
				if (typeof callback=='function')
					callback(target, elements);
				if ($.include.count.o==$.include.count.i) {
					while($.include.call.length) {
						var exe = $.include.call.shift();
						$(exe.elements).unbind(exe.eventType);
						exe.success(exe.target, exe.elements, exe.eventType);
					}
				}
			},
			img:[]
		}
	);
	$.fn.include = function(eventType, options) {
		var selectors = $(this);
		if (typeof options != 'undefined') {
			$(this).one(eventType+'', function() {
				if ($.isFunction(options.complete))
					options.complete(this, selectors);
				$.include(options.url, options.success, { target: this, elements: selectors, eventType: options.eventType});
				return false;
			});
			return false;
		} else {
			$.include(eventType.url, eventType.success, { target: this, elements: selectors });
		}
	};
})(jQuery);

// Loader Plugin
(function($) {
	$.fn.isIE6 = function(callback) {
		($.browser.msie && $.browser.version.substr(0,1) == 6 && typeof callback == "function")
			?callback($(this))
			:null;
		try{document.execCommand("BackgroundImageCache", false, true)}catch(err){};
		return this;
	};
	$.extend($.include, {
		loadingBG : 'include-loader.gif',
		loading : function(type) {
			if($('#jquery-include-loader').size()<1) {
				$.include($.include.loadingBG);
				$('
')
					.attr('id','jquery-include-loader')
					.css({
						'-moz-border-radius':'10px',
						'-webkit-border-radius':'10px',
						'background':'url('+$.include.loadingBG+') no-repeat 50% 50% #333',
						'border':'2px solid #666',
						'float':'left',
						'font-size':'0',
						'left':'50%',
						'padding':'25px',
						'position':'fixed',
						'top':'50%'
					})
					.isIE6(function(obj){
						$(obj).css({'position':'absolute'});
						$(window).scroll(function(){
							$('#jquery-include-loader').css({'margin': $('html').scrollTop()+'px 0 0 '+$('html').scrollLeft()+'px'});
						});
					})
					.hide()
					.appendTo('body');
			}
			if (type=='show') {
				$('#jquery-include-loader').show();
			} else if (type=='hide') {
				$('#jquery-include-loader').fadeOut();
			}
		}
	}
	);
})(jQuery);