If You work with MSSQL Server 7.0/2000/... under Windows and use non latin Encoding then better To use PDO_MSSQL until PDO_ODBC bugs will be fixed (MSSQL ext far more stable and usabe for PHP versions <=5.1.2).
If your MSSQL connection use strings in OEM encoding (cp866 for russian charset)
1. Run Microsoft Server/Client Network Utility on work PC and UNCHECK "DBLibrary options"/"Automatic ANSI to OEM conversion"
2. Restart Web server if needed.