Blocking referers shouldn’t be the job of a firewall. A local proxy such as The Proxomitron (my favourite, a very powerful program) or Webwasher will block them.

The Proxomitron can be downloaded here
www.proxomitron.info/files/index.html

www.proxomitron.org

has a list of other local proxies (including Webwasher).

Delta.

Edit: added links.