Nt Networking

I have a network of NT plateform. We have three floor of networking. Ground floor is for Internet users. First floor is for developer & second floor is for administration. All the machine is connected to a single network .We have a single ntserver at third floor for administrator & all other machine at first & GND floor is Windows 95& 98. Now I want to manage the network in such a way that ground floor machines cannot access the first & second floor machines. Second floor machines can access the third floor machine but cannot GND floor machines & Second floor machines are able to access the entire network.I need urgent help & solution for this type of scenario. I am very grateful to all of you who provide me proper solution.

Thanks