Using LinkSys Router As Switch To Extend Network?

I have a new Siemens router and have set up my old LinkSys router as a switch (set DNS outside the IP range of the primary router, disabled DHCP server, connect LAN to LAN port).The SSIDs are still different. As a result each device now sees 2 networks and although internet GW is available from either connection, not al resources are shared across the network. There is one driveshare (with wired connection to the secondary switch) which cannot be seen by some of the wireless resources on the same secondary network.Questions:1. How can I set up the NW config such that it is seen and behaves like one physical network, anbd roaming devices pick up the signal from the strongest access point?