Microsoft has made available a community technology preview (CTP) for Windows Thin PC, which is a locked down version of Windows 7 designed to help repurpose existing PCs as thin clients extending the life of existing hardware.
Although the final release of Windows Thin PC will be provided as a benefit for Microsoft's Software Assurance customers, Microsoft has made this CTP available in public for evaluation.
This CTP version includes some new features such as
RemoteFX support for a higher fidelity hosted desktop experience;
it supports System Center Configuration Manager, to help deploy and manage WinTPC images; and the write filter support helps prevent user and application writes to disk, thereby improving security at the end point.
More inforamtion is available on the CTP download site