Since this is a Development Release, it is available in the Downloads area in the section marked Development Releases and only a manual installation (zip archive) is available. The instructions to install the build are included in it, and are also available at this link: http://www.myeclipseide.com/PNphpBB2+file-viewtopic-t-3424.html
We encourage everyone that’s interested to try the build out and provide feedback to us, but request that you do not use it in a production setting as it is not a fully QA’d production release
You’ll need a fresh Eclipse 3.0.2 (not 3.0.1, not 3.1M1-7, only 3.0.2) installation and JDK 1.4.2_05+ or JDK 1.5 on Windows and Mac, and *only* JDK 1.5 on Linux.
Upgrading from a previous release
Basically, you can’t for this one, but for future milestones and 4.0 GA you’ll be able to upgrade your 4.0M1 installation using the Eclipse update manager, so it doesn’t hurt to jump in early.