Download the latest version of Proj4js here

The library is distributed as a .zip file and is available from the attachment below.

Unzip this file in a web-accessible directory and then include the file proj4js-compressed.js in your web page. See the UserGuide for more details.

The SVN repository for Proj4js is at:  metacrs/proj4js

Some example Proj4js definition files can be found in the proj4jslib/defs subdirecotry.