2000 network setup 2 questions

i have a nt 4 domain about to be migrated to win 2k. i have 8 branches connecting via VPN through isdn lines and t1s. each branch has a soho firebox which assigns ips for that branch and acts as their dns for each branch. Our main branch in NY has a soho firebox 2 and our ISP provides dns via the firebox, our nt 4 machine provides wins and dhcp. so how do i configure my win2k server to act as the AD directory, Act as the DHCP server, and wins but keep the DNS under the firewall. Also keep each branch the same way but still act as part of the AD ?