A brief note on the NodeJS blog yesterday revealed that Microsoft is partnering with Joyent to assist in porting Node.js to Windows.
As a result, Node will be available as a standalone executable (via node.exe). Importantly, this will run on systems as old as Windows Server 2003 and as new as the Windows Azure platform. Whilst it is currently possible to run Node.js under compatibility layers such as Cygwin, the additional installation steps and requirements put most people off from experimenting with the platform on Microsoft platforms. In addition, Node.exe will be supported and be available from the NodeJS site rather than a proprietary Microsoft hosted application.
The change is likely to require some reorganisation of the Node.js core, and whilst it won't affect other platforms directly it may delay the release of a 1.0 version until the reorganisation is complete. It is also not clear whether the Node Package Manager, which was recently released, will have any shell-script like dependencies which would need to be addressed (such as the install script) in order to run on Windows.
Microsoft is betting heavily on HTML5 with IE9, and sees the increase in JavaScript a good reason to invest in NodeJS. And by making it available on the (Windows) server side, it can only help their plans for the Azure platform.