Please help with planning a trip to Europe/UK?

My friend and i are planning a trip to somewhere in Europe/UK when we graduate (April 2011). We don;t know much about Europe/UK because we are from the USA (Boston area) and need help. We think we want to go to Edinburgh. Any recommendations, websites, or anything is helpful, thanks. We will be 18 and 19. Please keep in mind its our first time traveling without family! Requirements: Speaks English, Don;t need to rent a car, Not to expensive, and a lot to do in one area.