I am editing a film shoot in HDV and for tV purposes I need to broadcast in SD but I don't want to lose 16:9 format. I am working in Final Cut pro 5.1.1
I really don't know how to do that without losing quality or losing the minimum.

Edit in HDV and then import the entire sequence to a DV timeline set to anamorphic. You'll probably have to render the whole thing but it should be good to go.