Yes, it is possible to block any website in your PC. Firstly browse the Internet, go to Tools and click to get the pull down menu and then select Internet options from the window "General" tab, click the buttons delete cookies,and also delete files, then open the tab Privacy click Sites after that you should type the address of the website you want to block including "http://www."clik the "Block Button" and last click ok.
You have two methods to do so.
The first method is to use the built-in parental control in the windows XP, and the specific steps are here:http://www.ehow.com/how_2033277_use-parental-controls.html
The second method is to adopt third party parental control software, such as anykeylogger for win, which allows you not only to block sites, applications, set time limits of the Internet use but also to monitor computer activities including screenshots, visited sites, used applications, etc