Northwest and Continental DO NOT have reciprocal for preferred seating. I am a NW Platinum and I have NEVER been able to get preferred seating on a Continental flight, whether I've purchased it outright from Continental or whether it's a Northwest codeshare. This works both ways. Frankly I'd be really unhappy if you told me that NW gave you elite seating considering that I've been told by CO that if I want elite seating on CO flights I should change programs!!!

Also I have problems getting NW seats with online booking for flights more than about 30 or 45 days out. I regularly make these reservations online and call to get my seat assignments.