The error you are getting is because there is no ODBC drivers installed for your PHP client. You would require downloading the drivers from any site on the internet.
Following steps can be performed to download the drivers:
Download the drivers from http://www.easysoft.com/cgi-bin/account/login.cgi after registration or alternatively check the ODBC-ODBC Bridge Client platforms
(http://www.easysoft.com/products/data_access/odbc_odbc_bridge/index.html#platforms).This allows you to access drivers on a remote machine.
2. Install the drivers on the machine where PHP is installed.
3. Refer to instructions athttp://www.easysoft.com/products/data_access/odbc-sql-server-driver/manual/sql-server-toc.html to check the environmental variables what values to be set up for LD_LIBRARY_PATH, LIBPATH, LD_RUN_PATH, SHLIB_PATH depending on the driver, platform and linker.