In the desktop computers that are already connected to the wireless, do the following:
1) Click on the wireless icon in the notification area (system tray), it'll show the names of all the wireless connections detected. Your home connection (to which you are connected) will be in bold with the status "Connected". That'll give you the name of the network.
2) To locate your key, just right click on the connection (that you saw in 1), click on Properties, then click on Security tab. Check the box "Show characters" to reveal the network security key.