Whether or not a wifi network requires an encryption key (password) is not related to the operating system (Windows) but to the configuration set up in the router.
In Windows XP, after you select a wireless network from the “Choose a wireless network” screen and click the “Connect” button, if the wireless network is secured, you will get a pop up window asking you to enter the password twice.
Perhaps you should start at the beginning and explain your problem. Don’t forget to include the make, model, and hardware version (if any) of your wireless router.
It would also help us help you if you provide the particular model of your Dell Latitude.