Give the server a static IP, not DHCP.
The server, if a domain controller, will be running DNS
Add the IP of the Server as the first DNS entry on any client on the network you want to communicate with it
Add the IP of the Linksys as both the gateway IP(which it should be via DHCP), and as the second DNS server
This way any client wired or wireless that is connected will be able to use the linksys as the gateway to access internet and do internet DNS lookups, and will be able to communicate with the Server for domain things, like group policy, etc