Thomas,
Its only available to customers that have ordered a subscription to MyEclipse. Something that might help you evaluate MyEclipse is if you installed Eclipse 2.1.2 temporarily and downloaded MyEclipse 2.7RC2 and installed it, used it for a few hours (or days) on your project and see how well it adapts for you. If you like it, the 3.7RC2 version is the same functionality, just built ontop of Eclipse 3.0M6.
The ME team tries to keep the 3.x releases up to date, but because it is a preview intended as a curtosey and not their premier product, its not a good representation of the stability of the MyEclipse product, that is why they only expose the 2.x stable series for people to evaluate.