How can I split my home network (with WIFI) from my home office network?

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http://serverfault.com – I have a small business, and I don't feel very secure with network. I have a router, and I share the same network for my home and office. So, I have a wifi connection and I don't want to endanger my code server with wifi access. Can anyone suggest an affordable option to keeping wifi and network for my house, and creating a different network (closed access) for my office that do not have wifi (I have a VPN connection by the way). (HowTos)