I encountered this problem as well with a camera that actually shoots video in wide-screen (FCE would compact it giving it a "stilted" look); which was one of two problems I had when I first started to use FCE (yesterday), both of which I solved with iMovie. The first, which I shall briefly mention, is that my camcorder interfaces with USB, not Firewire, so I had to import the movie clips from my camcorder with iMovie (ver. 7.1.4). iMovie preserves the 16:9 aspect ratio if one tells it to.
At first, I used the files iMovie would make for its own use (the files in the "Event Library"). FCE would import these, but it would squash them into 4:3 every time. After looking around on the internet--including this thread--I did more experimenting.
I noticed that if I imported a movie that was exported as a wide-screen Quicktime movie (such as the graduation video I made for my cousin using iMovie), FCE would rightly treat it as a wide-screen video. What this means is, if you import your clips from your camcorder into an event, collect all the clips you want to edit into an iMovie project, then export the project "using Quicktime", you can then import that with FCE and edit it in wide-screen format.
The manner in which you export it depends on how fast your computer is or how much time you have: on my 3.06 GHz (Intel core duo) iMac, it took 2 and a half hours to export a 13 minute video (16:9, standard def.) in an uncompressed Quicktime movie with the quality settings the highest. Determine which file format is right for you if you do not quite have the time to enjoy every clip in its uncompressed, no-loss format.