The optional, add in elisp packages such as Gnus, Mew, WanderLust, BBDB, psvn, tdiary-mode, AUCTeX/LaTeX, Elscreen, emacs-w3m, session, Sudoku, etc (more), and ImageMagick integrated installation make this a very simple to install Emacs on your Windows box.
Meadow 2.x corresponds to Gnu Emacs 21.4 and is the latest stable version.
Meadow 3.x corresponds to Gnu Emacs 22.0.50 CVS HEAD and is pretty stable, but not labelled stable.
Installer and info/help pages have both English and Japanese counterparts. Installers are found at installation page, just click on setup.exe or setup-ja.exe.
The Meadow Wiki offers an overview of the additions to Meadow over the official Windows port: Detailed configuration and enhancements
EmacsW32 is another Windows-based effort, with both source (C and Emacs Lisp) changes, and an installer for both program and file associations and even supplemental Unix utilities. EmacsW32 also changes Emacs default keybindings to something easier for the Windows (perhaps leveraging the CUA mode). It seems EmacsW32 is more out-of-the box friendly towards the Windows user.
Meadow on the other hand does not attempt to change key bindings, do file associations or add Unix utilities (you need to add a GNU compatible diff, for example). Perhaps most significant is the support for the Microsoft Input Method Editor (MS-IME) which is important for CJK (Chinese Japanese Korean) users that are used to OS-enhanced language input. Meadow also has a alternative way of setting fonts (the original method is still supported). Meadow uses a Cygwin-like installer for the program and add-on packages. You can install, upgrade and de-install at a click. It also includes ImageMagick so you can see more graphics formats inside Emacs.