You don't get authenticated when joining a workgroup so there should be no problem specifying the workgroup name. You will only be able to browse other machines in the workgroup if the workgroup name exactly matches the other machines and your I.P address is on the same subnet.
How are you assigning the I.P addresses ? (DHCP ?)
Can you ping the I.P address of one of the other PCs ?
Are you using some sort of WEP, WPA for the wireless ?
article help ?