I was just poking around, and maybe try VideoBlend? I know Blender has video editing functionality, but the learning curve might be higher than what you're looking for. I see some open source solutions, but you'll need to install using something like brew or macports to install.
Another thing to do is download Adobe Elements and just use it within the trial period. Adobe's trials are fully functional for 30 days.
I take it you got your Mac used or something which is why you don't have iMovie? Why not just download (torrent, news, etc) the iLife DVD that was supposed to come with your Mac? Or buy a used disc off eBay for a couple bucks. Which Mac do you have?