OS X :: Searching A Good Video-editing Program?

I want to use iMovie, but whenever I import my HD image, it makes the quality worse, and the radial gradient looks horrible. Here is the image I'm trying to use: [URL]

here is what it looks like once imported into iMovie '09: [URL]

Is there a plugin for iMovie to fix this or something? I would you Final Cut, but my computer is slow enough, and adding heavy video-editing applications like that would not be good. Especially since I've had to replace my hard drive twice in the past year.