From OpenNMS

On February 10th, 2006, we moved to a new wiki based on MediaWiki. You probably ended up here by following a link to a page on the old wiki, but all hope is not lost--we migrated over effectively all of the old content.

You can most likely find what you are looking for by using the search box on the left side of this page (or any page in the wiki, for that matter) or going to the Main Page and looking around from there. The old wiki is still alive for a while in case you can't find what you need on the new wiki. The old wiki is now dead and gone.