swarfmaker
With sme in server and gateway mode do the following:
You need to totally reconfigure your modem/router into Bridged mode, which means that all signals pass straight through.
Disable DHCP server & Firewall & QoS, and any other functions in the router, as sme server will now be your router.
In sme server login as admin and run Configure this server and enter your ISP login details or whichever type of setup your Internet connection is.
Enter your domain name FQDN or at least enter a fake domain name in the form mydomainname.com, it's far better to use a free name from dyndns.com if you don't have an existing real domain name
Enter your WAN IP if you have a static IP, otherwise configure for pppoe or whatever.
Enter a LAN IP of 192.168.1.1 (or the same as what your router LAN IP used to be).
Enable DHCP server
Rearrange your physical network to be
Modem (bridged mode) -> WAN NIC -SME Server-LAN NIC -> 8 port switch -> PCs, VOIP fone, Network Printer, any other devices
Run the test Internet connection from admin console, swap NIC cables if necessary
Go to server manager (via a workstation) and set the DOMAIN/Workgroup name & enable Domain Controller if needed
Configure other settings