Peer-to-peer would be the normal way to run a small network. It simply means that all three systems are linked together to share data, printers, internet access - as required - but all of them are independant in their operations - none of them are the central repository of all the data/programs.
You need a Hub - or better, a switch - which will come with at least 4 inputs. In each computer you have a NIC (network interface card) - and a cable to the hub/switch.
Windows has all the software required to do the sharing - though it requires some setting up.
You can also do the same thing by wireless - it's more expensive, but can be more flexible.
If you want to share a broadband net access, this requires the use of a router - which can have the hub/switch built-in, whether it's cabled or wireless.
This is just a simple outline - it's not difficult, and there's tons of information about how to do it on the web.