Well, there are several things you would need to do. The computers all need to be within the same workgroup, which is usually defaulted to MSHOME. Since the network is already setup, the workgroup is probably the same anyways. So all you should have to do is right click on the folder that you want to share and click "Sharing and Security". Then, under Network Sharing and Security, click "Share this folder on the network" and type in the box what name you want the folder to show up as on the network. Then just click okay. To access the folder on the other computers, all you should have to do is click start, then My Network Places. On the left, find View Workgroup Computers. Click that, then it should bring up a list of computers. Just click on the computer it is saved on and you should be able to see and use the files in the folder.