How do you route between 2 ip networks

We are a county sheriff’s dept. We have a intranet network running on win NT for a small office. We want to connect to our county wide area network which is also running on win NT. We have a fiber cable strung and ready to connect the two but everytime we connect my pdc to the wan my pdc tries to take over the wan. some one told me to try winroute, others said I need a firewall, still others say I need a router with connections for rj45 and fiber. All of our intranet is connected via cat 5with rj45s. Any EASY suggestions?