Router config
 

I live in a community with a local network to which all the members are connected. When I bought my router (Dlink DI-524), the guy came round to configure it to work on this network.
I've since become more interested in networking and found that my router is actually being used as a switch (see attached jpg).

My router is connected to Router A via my LAN port 1, not via the WAN port and my DHCP is disabled. My computers get their IP's from router A. I assume that the IP's are assigned according to each computer's NIC, as the IP's are always the same for each of my machines. What bothers me is that I can see my neighbors' computers in my workgroup and I suppose they can see mine (obviously there are passwords involved, but still..).

What I would like is for my router to be the entrance/exit to the community network for my computers so that I am not on a mini-network with my neighbors.
I tried reconfiguring my router to do that (router A to WAN, enable DHCP), but router A kicked me off the network and I had to get the guy round to fix things up ($$$) as I have no access to router A.

Everything works right now, but I'm not happy with the setup as it doesn't seem secure and I'm not using the functionality/firewall on my router. Is there another configuration which would make me happy without screwing up my neighbors' connections?

Dont use DHCP on your WAN interface on your router - use a static configuration, one that is currently assigned to one of your workstations. Then, unplug the connection to his router from your LAN switch ports and plug it into the WAN port.

For instance, if one of your workstations is being assigned 192.168.1.115/24, then statically assign that to your WAN interface.

If he is using MAC address filtering and your switch is still being blocked, then record the MAC address from one of your workstations and see if you can apply it to the WAN interface of your router.

If you cant do that, then tell him your NIC went bad, had to buy a new one, and give him the MAC address of your WAN port as the "new nic" mac.

I tried your first suggestion. My router's WAN has the (static) IP that previously belonged to one of my boxes.LAN is configured for DHCP and router A is plugged into the WAN port.
So far everything is working, hopefully it will stay that way.