How do you lock a wireless via a network key, to prevent other people using it.

You need to access the Router web interface and set the wireless security on
the router first then Write down the WPA/WEP key you will create exact on a
piece of paper then access the other PC that will connect wirelessly  to the
Router and locate the SSID name of your wireless Network and Double click you
will be prompted for the key.
Here are some links will help you to know how to assign a security Key:

Using a Wireless Laptop at Work and at Home By Charlie Russel http://www.microsoft.com/windowsxp/using/tabletpc/expert/russell_tabletlaptop.mspx

Set up a wireless network
http://www.microsoft.com/windowsxp/using/networking/setup/wireless.mspx

You configure the security setting on the Wireless source, and then you do
the same exact settings on the Wireless Computer.
From the weakest to the Strongest..
No Security
MAC
WEP
WPA-PSK
WPA-AES
WPA2
-------------------------------------------
Wireless Security - <http://www.ezlan.net/Wireless_Security.html>
The security must be set according to lowest capable Wireless component.
I.e. even most of you Wireless are capable to do WPA2, but one device is
only capable to do WEP, the whole system must be configured to WEP.
Jack (MVP-Networking).

Show quoteHide quote

unwanted networks
Lost DSL Connectivitiy
Reconnected computer can share network resources but can't be seen
DEATH OF THE INTERNET
xcopy returns "Invalid drive specification" (w/ out the quotes)
routers
WLAN and LAN -- can't access internet
Can't access internet.
Sharing Files &/or Printers over Multiple Workgroups
Can't browse on one but can on the other?