Jquery: Getting the size of an element loaded with ajax

The script below loads content into a lightbox window.

I am trying to figure out how to calculate the height of the box after the content is loaded into it.
It currently is finding the height prior to loading causing a problem with the vertical centering

Here is the page:
One Equity Partners :: All Companies

Thank You E

	$('.more_info').click(function(){
				
				
				
				popout="<div id='lightbox_pop_out'></div>";
				lightbox="<div id='lightbox'></div>";
				$('body').prepend(popout+lightbox);
				
				popout_id=$(this).find('a').attr('id');
				
				$.ajax({
   					type: "POST",
   					url: "/application/view/content/portfolio_pop_up.php?portfolio="+popout_id,
   					data: "name=John&location=Boston",
   					success: function(msg){
     					$('#lightbox_pop_out').append(msg);
     					
   					}
 				});
 				
				$("body").css("overflow", "hidden");
				
                               //center lightbox
				w=$(window).width();
				h=$(window).height();
				
				lw=$('#lightbox_pop_out').width();
				lh=$('#lightbox_pop_out').height();
				
     					
     			        if(lh<h){ ptop=(h-lh)/2; }
				else { ptop=10; }
				left=(w-lw)/2;
				console.log(lh);
				$('#lightbox_pop_out').css({'top':ptop,'left':left+'px'});
				$('#lightbox_pop_out').fadeIn('fast');
										
				return false;
				
			});

I figured it out


$('#lightbox_pop_out').ajaxStop(function(){
					w=$(window).width();
					h=$(window).height();
				
					lw=$('#lightbox_pop_out').width();
					lh=$('#lightbox_pop_out').height();
				
     					
     				if(lh<h){ ptop=(h-lh)/2; }
					else { ptop=10; }
					left=(w-lw)/2;
				
					$('#lightbox_pop_out').css({'top':ptop,'left':left+'px'});
					$('#lightbox_pop_out').fadeIn('fast');
				});