Most notebooks with integrated Webcams are normally shipped with a preloaded Webcam Utility. Have a look under Start (Or Vista Circle) - Programs.
Also, what do you want to use the camera for ? - Webcam Chat, Taking still Pictures ? - Webcams such as those integrated into the top of leptop screens are only switched on by appropriate applications. If you don't find one on your machine, then I suggest downloading "Windows Live Messenger" - Microsoft's ap. for general Webchat, or search on google for another if you prefer.