Microsoft and HortonWorks have announced Hadoop on Windows and Mark Smith at Ventana Research wrote a nice blog post giving an overview of Hadoop on Windows.  Some key points:

1. Microsoft HDInsight Server and Windows Azure HDInsight Service are built on Hortonworks Hadoop Data Platform and make Hadoop readily available on Microsoft Windows. This strategic alliance helps IT organizations bring the power of Hadoop to Microsoft platforms. The Beta is now available.

2. Part of Hortonworks approach is that new advancements are contributed to the open source community where other developers and organization can contribute and help or use it once finalized and ready for distribution. This is a much different approach than others in the market who source Hadoop from the community and make proprietary extensions to it or embed it in their software and sell the license to the customer.

3. Hortonworks worked with Simba to provide a Hive ODBC connector to support SQL-92 access from business intelligence tools.  Microsoft Excel can easily direct access to Hadoop through SQL which opens up further support for a large number of organizations.