Canonical announced the second maintenance release of Ubuntu 6.06 LTS which is including several Security Fixes and some extra Hardware Support for servers.
Ubuntu 6.06 LTS has the longest support period until June 2009 for Desktop Users and June 2011 for Server Usages.
By the way, if you already installed Ubuntu 6.06 LTS, you don't need to download the newer version. All you should do is to run "sudo apt-get update" and "sudo apt-get upgrade", and you will have the newer version.