Microsoft Outs Free 90-Day Evaluation of Windows 8 Enterprise Edition for Devs
Microsoft has a launched a 90-day free evaluation of Windows 8 Enterprise edition so that even developers without TechNet or MSDN subscription can download it from the Windows Dev Center developer downloads page.
However, before you can start porting your apps on the new Microsoft OS, you also need to get the newly-released Visual Studio 2012. A Visual Studio 2012 Express edition is available for free but it can only work with Windows 8-style apps. A full version of the said developer environment is available to MSDN subscribers. The new .NET Framework 4.5 RTM was also released to make it easier for developers to port those apps.