Hi,
Try the Parental Filter from ecommsec. I have used it on a couple of pc's, for kids. It can sit hidden and can be directed to display any page or site if you try to visit a site containing banned content or words.
Its free and small and did not seem to impact on the browser perormance.
Look here
http://www.ecommsec.com
Or here
http://www.tucows.com/preview/336406
Hope that helps your problem .. If your dad asks why no porn just say the ISP must be blocking content.. hehe . ;o)
Good luck.