If your intent is simply to protect your computer from damage, but still allow Mr. Porn to view his websites, boot from a Linux LiveCD and do not mount any harddrive partitions.

If you want to block Mr. Porn and turn him into Mr. Family, I hate to say it, but nothing much is going to work for you. Unless Mr. Porm is exceedingly computer-dumb and you are exceedingly computer-smart. It would be trivial to bypass anything you might set up. Mr. Porn could simply choose to boot with that same Linux LiveCD mentioned above and go surfing away, no matter what you set up on the computers harddrive.

If you want to allow Mr. Porn to view his websites, and you want to protect your computer, and you want it to be running Windows - sorry Charlie, no way on that one. You can add a ton of software, causing all kinds of conflicts and slowdowns, and end up not much better than you were in the fist place.