I really don't understand what you need. Do you need an application to block websites or do you need an application to access blocked sites? For the first case i recommend Cyclope Internet Filter http://www.cyclope-series.com/... On the other hand, if you need an application to unblock the websites than i recommend IP Privacy http://www.privacy-pro.com or IP Hider http://www.allanonymity.com .

You can do like this:
Step 1: Click the Start button and select Run. Now type the following text in that Run box:

notepad c:\WINDOWS\system32\drivers\etc\hosts

Step 2: You will see a new notepad window on your screen containing some cryptic information. Don’t panic. Just goto the last line of the file, hit the enter key and type the following:

127.0.0.1 orkut.com
127.0.0.1 facebook.com
127.0.0.1 myspace.com

Save the file and exit. That’s it. None of the above sites will now open on your computer.

You can block as many websites as you like with the above technique. If you want to remove the ban later, open the same file as mentioned in Step 1 and delete the above lines.

OR you can use also a blocking software like http://www.applicationblocker.com