Well this question should be in the Internet and Networking forum but here goes.
Right click on the desktop Network Neighborhood icon and go into Properties and under Identification tab make sure that all PC's have the same Workgroup name. Then under the Configuration tab click the File and Print Sharing button and tick at least the "I want to be able to give others access to my files". Now you will need to go into My Computer and either right click on a drive or folder and click on sharing then click Shared As. Once this is all done you should be able to see other PC's on the network.