For documentation and tips go to the ERC homepage at the EmacsWiki. The Savannah project page is here.
Please report bugs to the erc-discuss mailing list.
The latest version is 5.1.4. You can download it from the GNU ftp server.
Nightly development snapshots are also available: erc-latest.tar.gz or erc-latest.zip.
ERC will be included in the next release of GNU Emacs.