Windows 8 consumer edition is available to download now, you can get it directly from Microsoft.  This version of Windows has a new GUI (graphical user interface) but the “old style” windows is still running under neath.

You can download it from Microsoft (either as ISO or auto-download package, which includes info how to boot via USB if required)

This consumer edition expires January 2013, so it will give a good amount to test it out, and time for developers to write new apps for it, before the final release early next year.