You are online via the WiFi network and your Windows XP computers are all patched up and ready to be found by your Windows Vista PCs. That leaves just one more step to take, and it is a simple one. For some reason, Windows XP and Windows Vista use different default names for workgroups, which means XP computers think they are on a different network than their Vista network-mates. Fortunately, this is easily remedied.
Start with the Windows XP computers on your WiFi network. Go to the Control Panel from the Start menu and select System. The System Properties dialog will open. Go to the Computer Name tab and click the Change button down at the bottom of the dialog. Then, just type in a name for your workgroup, making sure you note the exact spelling used, as you will need to enter the same workgroup name on the Windows Vista computers.

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When you have changed the workgroup names on the Windows XP computers, do the same on any Windows Vista machines. Click Start and type System in the Start Search box. Click on System in the Programs list. The System window will open. Select Advanced System Settings in the left pane of the window to open System Properties. Go to the Computer Name tab and click the Change button. Enter the same workgroup name used on the Windows XP machines and apply the changes.

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You should now be able to find Windows Vista computers from Windows XP machines, and vice versa, on your WiFi network.