It is not completely obvious how to turn disable the router functionality on the D-Link DI-624 so that it only operates as a wireless access point. Here is the recipe, which I initially found on dslreports.
Connect to a LAN port (not the WAN port). Change the 'LAN IP address' to an unused IP address on your LAN. On Home | DHCP: Disable the DHCP server. On Home | WAN: Set the WAN port to Static IP and then configure the Static IP address to bogus values: IP address = 220.127.116.11 Netmask = 255.255.255.0 Gateway = 18.104.22.168 DNS = 22.214.171.124 Reboot the DI-624.