PDO mssql + multiple rowsets

Hi! I want to use PDO in my apps for connecting to several RDBSs, one of them, sql server 2000 and 2005. I tried to use as DSN something like "mssql:..." (as I've seen in the php manual pages) but I get a PDOException with the message "Unable to open PDO connection [wrapped: could not find driver]". I can work well with the mssql built-in functions (like mssql_connect, mssql_query and so on...) and even I can almost work perfectly using in my dsn "dblib:...". So first question: is the PDO's driver "mssql" deprecated or is it me doing something wrong in the PHP installation? BTW, I use php-5.2.1 In case that the answer to the first question is that "mssql" is no more used as a PDO driver, I have a problem... I have stored procedures in sql server that return multiple rowsets, I've seen that PDO offers functionability to manage this, but not for the dblib driver... if I try to use the $stmt->nextRowSet() method, I get an exception like "Driver does not support this function: driver does not support multiple rowsets" What can I do then to work with my stored procs? Thanks in advance