The difference between mssql_connect and sqlsrv_connect

I just changed the connection driver (extension) from mssql_connectto work with sqlsrv_connect. Unfortunately, everything does not work the way I wanted. I would appreciate it if someone would tell me what happened and how I can fix it.

Code Excerpt:

//a oracle DB moudle with a generic functions such as 
//db_connect() db_query()

/// turn on verbose error reporting (15) to see all warnings and errors 
error_reporting(15);
//generic DB operations

// Global record . for using in 
$curr_rec = NULL;

function dbok($res)
{
    if($res==false){
        echo "DB error: "."FIXME need error mesg"."\n";
        exit;
    }
    return $res;
}

function db_now_expr()
{
    return "getdate()";
}

function db_is_connected($dbh)
{
    return $dbh>0;
}

function ensure_connected($dbh)
{
    if(!db_is_connected($dbh)) die("DB is not connected, operation failed");
    //echo "DEBUG: hdb=$dbh"; 
}

//connect to given database 
//return handler to DB


function dbo_logon($dbserver,$dbname)
{

    $tsql = ??????? ====>>> what should i put here???? 

    $dbserver = "computername\SQLEXPRESS";
    $dbname = MY_Database_name;

    $connectionOptions = array("Database"=>"BULL");

    $dbh=dbok(sqlsrv_connect($dbserver, $connectionOptions));
    dbok(sqlsrv_query($dbname,$dbh)); 

    $stmt = sqlsrv_query( $connectionOptions, $tsql );

    return $dbh;

}

//close DB
function dbo_logoff($dbh)
{
    if(!db_is_connected($dbh)) echo("DB disconnect error");
    sqlsrv_close($dbh);
}

Here is the source code using mssql_connect:

//a oracle DB module with a generic function such as 
//db_connect() db_query()

/// turn on verbose error reporting (15) to see all warnings and errors 
error_reporting(15);
//generic DB operations

// Global record . for using in 
$curr_rec = NULL;

function dbok($res)
{
    if($res==false){
        echo "DB error: "."FIXME need error mesg"."\n";
        exit;
    }
    return $res;
}

function db_now_expr()
{
    return "getdate()";
}

function db_is_connected($dbh)
{
    return $dbh>0;
}

function ensure_connected($dbh)
{
    if(!db_is_connected($dbh)) die("DB is not connected, operation failed");
    //echo "DEBUG: hdb=$dbh"; 
}

//connect to given database 
//return handler to DB
function dbo_logon($dbserver,$dbuser,$dbpass,$dbname)
{
    // $dbh=dbok(mssql_pconnect($dbserver,$dbuser,$dbpass));
    $dbh=dbok(mssql_connect($dbserver,$dbuser,$dbpass));
    //error_log("connect to [$dbname]".date("His")." \r\n",3,"/tmpbull.log"); //DBEUG DELME
    dbok(mssql_select_db($dbname,$dbh));
    //dbo_exec($dbh,"alter session set NLS_DATE_FORMAT='dd-mm-yyyy //hh24:mi:ss'");
    return $dbh;

}

//close DB
function dbo_logoff($dbh)
{
    if(!db_is_connected($dbh)) echo("DB disconnect error");
    mssql_close($dbh);
}

Note that I had to change the authentication method from SQL authentication to Windows authentication, as it sqlsrv_connectuses Windows authentication instead of SQL authentication. Is it correct?