For documentation and tips go to the ERC homepage at the EmacsWiki. The Sourceforge project page is here.
The last version of ERC released on Sourceforge was 5.1.2. You can download it and older versions from the released files page. Newer versions can be found on the GNU ftp server.
Please direct all comments and bug reports to the GNU erc-discuss mailing list. The erc-help mailing list is no longer in use, but archives are available.