Give this a whirl
History: as you surf the web, the list of places you've visited is kept as your history. You can control how much history is kept by adjusting the setting found in Tools, Internet Options, General tab, History box, Days to keep pages in history setting. By making this a smaller number, perhaps a week or even just a few days, you'll make a significant reduction in the number of URLs that IE will show for auto complete. You can also completely clear history here, if you like. Alternately, if you would rather truly edit the history, press this History toolbar button, which will open the history window, and you can right click on any entry and select delete.