It isn’t easy locking down a computer especially if it is a public computer. If you own a business you already know the pains of locking down your computers from your customers, even your employees. When 
at home you have children or friends and family wanting to ‘borrow’ your computer to search the net or look at their email. How can you truly lock down your computers to only allowing certain applications or features and trust that no one is going to install programs or get any malware on your computer? There are some very popular ‘lock down’ apps that you can pay for but I like the free stuff :)
It would be worth your while to take a look at . SteadyState is a pretty granular app where you can block certain apps, features, or data all the way down to the user profiles :) A more detailed video of its features can be found on the site so feel free to take a gander. But here is one example: I created a new user on my home computer 
SteadyState is free for genuine Windows XP and Windows Vista computers. SteadyState will not work on Windows 7. To lock down Windows 7, you will need to play around with “Windows Live Family Safety