I have also had this problem. I have made sure all machines (two xp desktops, one xp laptop, one 7 ultimate desktop and one 7 home premium laptop) all have the same workgroup. I have rebooted. I have (when I could see the respective computers on the network) mapped network drives. All machines can access any mapped drive. However, on the list of network computers, my Win 7 machines can see each other but not the xp machines, and vice versa. I suspect this has something to do with the domain/workgroup distinction thing, but don't know how to set this so that it does not happen again. Once again, I at one point could see ALL the computers on the list. Please help!!