http://www.codecademy.com/#!/exercises/0 is a good place to start for basics. Once you feel more comfortable writing code, start looking at alternate languages and libraries such as C# with XNA, Python with Alice, Unity and UDK.
http://www.khanacademy.org/#computer-science has some talks/exercises for computer science and you can pick up some more University material from here:
http://www.openeducation.co.uk