I don't know whether the seat brackets are interchangeable between gen. 1 and gen. 2 Foci, I do know that the side air bags will be a problem. As I have said many times here, Focus air bags are model year specific. The 2006 SRS control module, beneath your center console, btw, is compatible only with 2006 model year SRS components. When I installed '03 SVT seats into my '05 ST, I had to swap the '05 side seat air bags into the SVT seats. In addition, I had to swap the seat belt buckle, and the pressure sensing switch in the passenger seat cushion which activates the passenger side dash (front) air bag.
Keep in mind that when the air bag light comes on, none of the air bags work.