It turns out that fellow challenger Juozas Kaziukenas also needs a connection between Zend Framework and SQL Server, so we have joined forces to create App_Db_Adapter_SqlSrv and associated classes. Juozas started a project on codeplex at http://zfmssql.codeplex.com/ and has enabled me to commit to the project too.

Rob based his implementation on this and has set up his application.ini file to use the SQLSRV adapter (example included).