jake,
load up the problem clip from the timeline into the viewer. In the motion tab look at the distort function. You can change the aspect ratio of the clip that is in the timeline. I imagine if it is anamorphic and the timeline is 4:3 then it will be set at 33.33. Change it to 0. have a play if this isnt the right way round.
FCP has so many setting which makes it very versatile, but sometimes difficult for the new user! Bacisally once you have put a clip in the timeline then any changes in the browser or the in clip settings wont affect the timeline. You have to load the clip up from the timeline, then change it. If the settings were wrong to start with and you have all the clips in the timeline wrong, correct one of them, then copy, and paste attributes to as maany clips as you want in one go.
hope this helps.
nick