to share a file or folder.
Go to My Computer and go to your file or folder you want to share (example C:\music). Right click on file or folder and choose Sharing. There may be a blue link on the top explaining what you are about to do. Click on it. Then click SHARE AS radio button and name it. The name will show on the other computers. There are other options which I don't know of memory, but I will when I get back from school.
As for the network ID, it's kinda hard to explain now, but basically your IP addresses should look the same on all computers except for the last one. (Your network ID is part of your IP address)
Go to START > RUN > type CMD. Then type ipconfig. You will get a basic list. The default IP address is 192.168.0.x, with x being any number from 1-254. If the numbers start with 192.168 then the third set may be different to the one I have here, but the first three sets of numbers should be the same on all computers.
For workgroup, Right click on My Computer, Properties.
Under Network Indentification, you should have Full Computer Name and Workgroup. The Workgroup name should be the same.