iMovie hangs when I delete events or clips. i think it got worse after installing Lion. Suggestions please? MBP

Hello, do you think you can help me . I have a canon 7d and when I go to I movie to edit after converting my clips , when I go to quick time and get the final results the footage is fuzzy I changed the settings to 1440+1080 and its worse . What should the setting be? I am filming in 24p