On the desktop connect the computer to the router by the Ethernet cable, now type 192.168.0.1 into a browser window. If asked for a user name and password use admin and password. In the left pane look for a section named wireless or similar wording (I can’t remember the exact wording). You should be able to see the SSID and the WEP/WPA key. Make a note of both of them.
On the Vista laptop go to Control Panel > Network and Sharing Center > Set up a Connection or Network (in the left pane) > Manually Connect > Next. Now type in the Network Name (SSID), select Security Type and type in the WEP/WPA key. There is more chance of a reliable connection if the key is typed in hexadecimal rather than as ASCII characters. You may also want to tick ‘Start this connection automatically’ and ‘Connect even if the network……‘ > Next. Lastly click ‘Connect to‘ and you should connect to the network.