windows xp po ang gamit ko po
Query the wifi router if you have one. By typing 192.168.1.1, you should be able to enter the router's menu.
Launch firefox or IE, then type the numbers above. You should be able to see in one of the menu items if there are several mac addresses using the router. If you're the only user, only your mac address should appear. I suggest you read up on how to set up WEP or WPA.
Doesn't matter if you're using xp or vista or win7.