How to setup 2 networks in one router. [closed]

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http://serverfault.com – I am tryign to setup 2 networks for my company. I need 1 network for the first room and another network on the second room. Each room can't access another room's computer. I have setup 2 workgroups for each room but it seems that the workgroup can't setup passwords. Every computer is in the same subnet with static ip. They all connect to a switch -> router -> modem. Router: Linksys WRT54G Switch: Intellinet Any thoughts? Thanks a lot. (HowTos)