how do you block a website on windows xp?

You block websites with your browser, not your OS. So what do you run to view the internet, Google Crome? Let's use that for an example. Upper right corner you see either a wrench or something, click on that and all your answers will be taken care of quickly.

1) In internet explorer, click Tools (in the top bar of the screen).

2) Go to internet options and click the Privacy tab.

3) Toward the bottom of the screen, click turn on pop-up blocker.