Announced at TechEd 2013 Europe by Brad Anderson, the R2 bits for Windows Server 2012 and System Center 2012 have been released as previews. Our sister site, Windows IT Pro, has the coverage and a list of all the download links. You can catch all of that here: Microsoft Keeps TechEd 2013 NA Promise, Releases Previews for Blue Servers.
SQL Server 2014 and Windows Server 2012 R2 are available to preview in a Windows Azure environment, along with being readily available for download, but System Center 2012 R2 is the only preview piece that is available solely as downloads. To help get your testing environment started quickly, Microsoft has also provided an Evaluation Guide, that aids in the setup and testing for an evaluation environment.
The Evaluation Guide download is here: Evaluation Guide for System Center 2012 R2 and the Windows Azure Pack
It’s available in both PDF and MS Word formats.