You could google for anonymous proxy servers and enter the IP into your network preferences, or you could download a handy little shareware program called NetShade http://www.raynersoftware.com/netshade/
It accesses a database of free anonymous proxy servers and will automatically configure your network prefs for whatever proxy you select. You can even have it switch servers after a certain time interval. It costs a bit much, $30 I think, so just use the unregistered version to access the list of anonymous proxy servers, pick one you like, and enter the IP in the proxy tab of your network preferences.
