Small store infrastructure - where to begin?

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http://serverfault.com – It looks like my older brother is about to change jobs - from lawyer to shooting range proprietor - and since I'm the family 'computer guy' I have the task of coming up with and setting up the in-store equipment. Only problem, I don't know how to start or where to look. I'm a web programmer, not an IT specialist. To that end, I figured I should ask the pros. Users: 3 (myself, my brother, and his business partner) Equipment: 1 Windows (likely 7) desktop for POS software, 1 Windows desktop/laptop for backroom use (bookkeeping, etc.) Other: ?? I'm looking for a reliable and, well, idiot-proo (HowTos)