This is a driver for CodeIgniter 1.7.2 to give support for SQL Server 2005 onwards (including SQL Server 2008).
I tested this on an old copy of thread-safe PHP 5.2.2 using the threadsafe version of the php_sqlsrv.dll driver, and it worked fine. It does state PHP 5.2.4 as a requirement, but I didn't run into any problems: your mileage may vary. The driver should also support PHP 5.3 if you are using the latest version of Microsoft's driver (version 1.1). Make sure that you read the requirements section in the Windows Help File (CHM) that comes with the driver, since you may need to get the Microsoft SQL Server 2008 Native Client (sqlncli10.dll) in order for it to work (regardless of which version of SQL Server you are running).
->num_rows() can be a bit of a pain. It needs a specific cursor type to work (which is
detailed in the manual). It should work by default since I have set it to SQLSRV_CURSOR_STATIC,
but I don't know yet if it will cause any performance issues. If you don't need to use the
->num_rows() function within sqlsrv_result.php I suggest changing this back to the
default of SQLSRV_CURSOR_FORWARD.
UTF-8 — The driver will connect using the UTF-8 charset if you set it as such within
your config. From what I have read, the UTF-8 support only works when you use parameterised queries, which
doesn't really 'fit' with how CodeIgniter goes about active record. For the time being, this will likely be
broken - I haven't had chance to test it yet.
system/database/drivers/sqlsrv and change your database.php
configuration file accordingly (set your dbdriver to 'sqlsrv')