If you're not installing into an existing Eclipse, you'll need one.
Eclipse Helios SR2, or
Eclipse Indigo
Eclipse JEE Indigo recommended.
Select Help>Install New Software..
Enter one of the Virgo update sites below.
Select "Virgo Tools" feature and click install.
Note, M4 is not quite here yet, so as of the moment you should use the snapshot build, not the milestone. As soon as M3 is formally released, this will change.
Many users will also want to install the M2E release at: <code> http://download.eclipse.org/technology/m2e/releases</code>. (e.g. in order to run the greenpages examples.)