1. You must have all computers connected to a router, hub, or switch. Which do you have?
2. You must give each computer a different name and join them to the same workgroup.
Start - right click on my computer - properties - computer name - change. Make sure all computers have different names but use the same workgroup name.
3. Create a user on each computer with the same name (ie all of my computers have "Rob as a user) and a password. This is not necessary but will make things easier.
Start - control panel - user accounts (the rest is obvious)
4. Create a nre folder on the desktop of each computer and share it. Again this is not necessary, but will give you something to look for when browsing the workgroup computers.
Create a new folder on the desktop (name it what ever you want like "Share") - right click on the folder - properties - sharing tab - share this folder.
5. Test, start - my network computers - view workgroup computers (you should noe see each computer in your workgroup as an icon) - click on a computer and you should see your shared folder.
There may be some more steps depending on if you are using a firewall and what type of connection device you are using. If you get stuck or have problems let us know where in the process you are haveing troubles.
Let us know how it goes.