first you didn’t provide the sites you want to block, then you have several ways of accomplish to this.
The best is to create a Proxy server with content management filter (<a href=”http://itknowledgeexchange.techtarget.com/it-support/tlbat-proxy-server-and-content-filtering/”>see this post on my blog</a>). In alternative you may want to create a BLOCKED ACCESS html page and then add the blocked sites to the C:\WINDOWS\SYSTEM32\DRIVERS\ETC\HOSTS file that redirects those sites to yout http://127.0.0.1/blocked.html file
Once again, consider the first choice as the only affordable one.
Don’t forget to visit my blog:<a href=”http://itknowledgeexchange.techtarget.com/it-support/”> If it has a plug, it’s IT stuff!!</a>