This can be a simple or challenging project depending on the requirements. If you are trying to get this done on the cheap then redundancy/fault tolerance is out of the question. Assuming your goal is to connect all offices over public Internet circuits securely your best bet is to procure some SOHO VPN/Firewall appliances. SonicWall is a good choice for SOHO since administration is graphical and simple and the price is relatively small. There are other appliance options such as Symantec and Firebox.
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