Slow Joomla

I have a Joomla site that is running very slow on its loading fase. I have connected to it the Mosets Tree directory system. I need someone to determine the reason for this problem and be able to fix it. I am sure its not an images problem, because i dont have any on the front page. The website is ([login to view URL]). When i load the website in IE8 i get the following error message "A script on this page is causing your browser to run slowly. If it continues to run, your computer may become unresponsive" The website frontpage was slow but i begun receiving this message when i added a new "city" with 234 sub categories in the list. If i remove the city with its subcategories, the error message goes away, but still the website is very slow. I think that the problem here is with loading the data off the DB.