How to connect my macbook to a wpa wifi? Help?

Hiya. I have a late 2007 macbook that is up to date with Snow Leopard. It is running on 10.6.8. My router is a WPA and for some reason my macbook won't connect to it! My macbook pro connects to it just fine and I know that this computer model will connect but there is a configuration I need to do. Does anyone know the specific configuration that needs to be done for it to connect? Thanks!