There is no php_mssql.dll in the WampServer. Moreover, this driver is not supported by PHP and is not distributed with Windows versions of the PHP.
You must download "Microsoft Drivers for PHP for SQL Server" (http://www.microsoft.com/download/en/confirmation.aspx?id=20098). This file contains vc6 / vc9 and ts / nts versions. It works well on two my projects.
regards
tk1
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