I've been using iMovie 6.0.3 for years. It's fine for the uses you mention, while Final Cut Express and Final Cut Pro are more complex. If you can get that version or earlier, do so. Later versions stripped away many of the more useful, and professional features. Here's something I found at Wikipedia <http://en.wikipedia.org/wiki/IMovie#Criticism_of_iMovie_.2708>, with which I agree:
iMovie 08 was criticized due to its drastic abandonment of some iMovie HD 6 features. New York Times reviewer David Pogue said "iMovie ‘08 is an utter bafflement... incapable of the more sophisticated editing that the old iMovie made so enjoyable...All visual effects are gone — even basic options like slow motion, reverse motion, fast motion, and black-and-white. And you can’t have more than one project open at a time."
Features removed included the classic timeline, the ability to create DVD chapter markers, support for plugins, and in-timeline audio adjustment and control. iMovie '08 imports to a much more limited set of video codecs and metadata formats than previous versions of iMovie or today's QuickTime Player. For example, QuickTime Player can be extended to support the FLIP Video 3ivx MPEG-4 codec, but iMovie '08 cannot. iMovie '08 also removed the ability to import DV footage. As a result, all resulting videos have lossy compression applied and there is no facility for managing full format video. The peculiar lack of QuickTime support means QuickTime Pro can edit a larger range of video than iMovie '08.