1. click "Final Cut Pro" drop down menu (in between "the Apple" & "File" menus)
2. Easy Setup
3. DV NTSC - Anamorphic
That should do it for you.
I have to say I had the hardest time trying to get my footage anamorphic when I first started using FCP about 7 years ago. It took me about 2-3 hours of trying to convert 4:3 footage into 16:9, going through google & then while I was screaming at my computer screen "I just need a check right here!!!" I hit my mouse button in rage & bam! check appeared in the anamorphic invisible check box area.
Apple can be so simple & easy sometimes, but very frustrating if you don't know that you can check an empty space. Would it have been so hard to put a radio button or empty box there Apple? ...ugh... bad memories