Magento Ajax Loading of Page Content Area

I am looking for a developer to customize the category pages of Magento website. What I need is that the content area of category pages is loaded by Ajax. When you click on a category on the main menu, the page has to turn a little black faded. It would be good to show a loading circle animation icon at the center. The page gets back to normal brightness with the new content of the chosen category. Please note that the url in the browser address bar should be changed while only the content area is reloaded, not the whole page. I have seen that many Magento themes are doing the same thing (Mostly for ajax filter on the layered navigation side bar). If you want, I can give you some references. I need this to be complete by Sat.