Your IT staff would install a "router". Then program it to your specifications.
As to files and such, all the usual IT work of PERMISSIONS will keep files from "flowing" around.
I need to know a quick and less expensive method to connect two networks together. I have an existing IP network with 2003 servers running DHCP,DNS,WINS and all the standard items. There is an existing router which is the gateway for a T1 connection to the internet. I need to create a 2nd network for a new department and am told to keep it isolated from the existing network due to the large files that will flow across this new metwork which could otherwise cause bandwidth problems on the existing network. The problem is that some machines on the new network will need to talk (transfer files) to servers on my existing network and they will also need to get to the internet via the T1. What is the least expensive router/way to connect this new network to my existing network? Recommendations on particular hardware would be extremely helpful.