Well, this is going to have to be a "consultative" reply...
How are all the computers getting out to the Internet, or is there some that aren't? If all are connecting to a wireless access point, for example, then the "infrastructure" is already there for you - but it may be a little bit slow. I prefer wired - speed is good as well as reliability. Downside of course is that if you don't already have it, you'll be running cables around.
Now.. crossing slowly from "infrastructure" to actual networking stuff... first, let's make sure all your computers are "behind" a router. They should be, since I am assuming you have more than one capable of getting out on the Internet. With the "file sharing" stuff running, you're best to keep any shared file locations BEHIND the router so that all but the most determined hacker won't be able to access them.
So that's the "hardware" part of the equation. Software - pretty easy... What operating system(s) are you running on each of the computers you want to network?
Finally.. do this quick test for me, to see if one of your computers can "see" another. First.. on the computer you'd like to designate as the "server", or computer that will serve as the central storage location, go to a command prompt (start, run, type in CMD and hit enter<-assuming you are on XP or higher), then type the following and hit enter...
hostname
That's the computer's name. Now on the other computer you want to "access" the server with, do the same "command prompt" and type in...
ping <hostname> (where <hostname> is what came back when you typed in the above command)
.. then hit enter. Tell me what it says...
Also.. tell me what kind of antivirus, anti firewall, "anti-going-to-get-in-the-way" (heh) software you are running. Chances are we'll have to make some "exceptions" to allow the computers to talk to each other properly.
Enough for you to figure out for now.. let me know the answers and we'll continue..
