Secure network in another network

[sswats]

I have 2 computers connected directly to a router and the internet. I'm setting up one of the computers as a server to provide a wifi service that's going to be open for people to use.

I've connected it to an access point and now just need to secure this computer and the network from any wifi intruders.

What is the best way to go about this? just a simple firewall?

 

[sswats]

Sorry I left a bit out. I'm installing a hotspot server. currently considering this software http://www.antamedia.com/hotspot/. If you click on how to setup it shows the diagram of whats needed.

but the PC we have now is used for business stuff I would like to keep safe.

My alternative is a separate PC and Broadband connection just for the hotspot setup. or is that unnecessary?