Which is probably the best is to login to the HG659 and change its LAN ip to match that of your local area network for example 192.168.1.100, disable its dhcp and plug a direct cable from its lan 1 port to your router assigning your local dhcp, it'll then handshake and your dhcp router will assign ips and route internet to any devices that connect to the hg659
Login to HG659 and go to internet/wan settings and disable its vlan tagging option or set to 0,
plug a cable from its wan socket to your DHCP router. it'll then pick up a dynamic ip from your router as a WAN IP,
This may seem like the easier option but your HG659 will view this like an internet source and will need to have its own DHCP server operating making a double NAT enviroment and will also be acting behind its own fire walls.