Pleasantville effect in Final Cut EXPRESS?

I am currently editing a film for a school project, and I really want to try and create a the pleasantville effect (main character is black and white, the rest of the film is colour), but it's becoming extremely difficult, as other parts of the set or characters are going black and white also. Do you have any tips for Fine tuning? (I am using Final Cut EXPRESS, not PRO so please DON'T give me tips for when using Final Cut Pro).