NW flights have a "preferred" section that is available only to elites and full-fare pax. The seats aren't really special, though, except that they're closer to the front of the plane. See http://www.seatguru.com for information about the best seats on NW flights (and most USA-based airlines).

As a WP elite I've been able to get SSZ on KL flights if I try hard enough (it takes the NW phone agents forever to get into the special KL computer system or whatever they have to do). So I'd assume FD elites would get the same treatment on NW flights.