PHP fatal error message

I am moving our sql database and files to a new server with php 5.  Our previous php is done in 4.  I am not sure what to update here, but I get the error message Fatal error: Cannot re-assign $this in /home/content/g/a/r/garrisongp/html/include/PHP_DBI.php on line 69  Below is the code for that particular file  
<?php

// $Id: PHP_DBI.php,v 1.1 2004/03/22 21:53:23 matthew Exp $

/*
 *  Database wrapper class basically, makes database calls
 *  to mysql and mssql tranparent to the other classes and functions;
 *  kinda like Perl's DBI, but not really :)
 *  
 *  This class will doubtlessly need to be extended as more functions
 *  are added to it and more database drivers are supported.
 *
 *  Found a nice way to keep this a (mostly) abstract class and not do a double
 *  method call on every call to this class! Turns out you can assign to $this
 *  in the constructor, so all we have to do is instantiate the subclass and assign
 *  it to $this, and boom, there you go. No need to keep the subclass around as
 *  a member and pass on all the method calls to it. Should speed things up significantly.
 *  
 ************************************************************************
 *
 *  HOW TO INSTANTIATE PHP_DBI OBJECTS
 *
 *  $DB = new PHP_DBI("Driver", $host, $database, $user, $password, $port, $DSN);
 *
 *  Where Driver is the name of the driver -- "Mysql", or "Pgsql" or whatever.
 *  Must match the name of the file the driver class is kept in.
 *
 *  $host will default to 'localhost'.
 *
 *  $port and $DSN are optional. The latter is used for ODBC connections.
 *
 ************************************************************************
 */

class PHP_DBI {
      /*
      * instance variables
      */
      var $dbh = 0;

      var $driver = '';
      var $sql_host = '';
      var $sql_port = 0;
      var $sql_user = '';
      var $sql_pass = '';
      var $sql_dsn = '';
      var $database = '';
      var $errno = 0;
      var $errmsg = '';
      var $error_reporting = 0;

      /*
      * CONSTRUCTOR
      * significantly different than the old monolithic Database.php. This time
      * around a connect string sort of like perl's DBI is passed in.
      * The first parameter must be the name of a driver in this same directory.
      * E.g., if you want the "Mysql" driver, the Mysql_dbd.php  file must be in
      * this directory. Or Pgsql_dbd.php or Mssql_dbd.php or whatever.
      */

      function PHP_DBI($driver, $sql_host = 'portfoliogar.db.5036119.hostedresource.com', $database, $sql_user, $sql_pass, $sql_port = 0, $sql_dsn = '') {
            if ($driver != $this->driver) {
                  $this->driver = $driver;
            }
            $DBD_name = $driver . '_dbd';
            $DBD_file = $DBD_name . '.php';
            include_once "./include/$DBD_file";

            $this = new $DBD_name($sql_host, $database, $sql_user, $sql_pass, $sql_port, $sql_dsn);
      }

      /*
      * CONNECT
      * generic connect function; connects to the server for the instantiated
      * database object
      * returns a connection object just in case it is needed
      */
      function connect() { }
 
      /*
      * PCONNECT
      * same as CONNECT; except for persistant connections
      */
      function pconnect() { }
 
      /*
      * CLOSE
      * pretty simple, just closes the connection
      * returns success or failure
      */
      function close() { }

      /*
      * DB_QUERY
      * Uses the interal db handle to submit a query to the database
      * returns the result id of the query
      */
      function db_query($sql) { }


      /*
      * FREE_RESULT
      * frees the previously obtained result set; RTFM if you need to know more
      */
      function free_result($result) { }

      /*
      * FETCH_ROW
      * just fetches a row and returns an indexed array, starting at offset 0
      */
      function fetch_row($result) { }

      /*
      * FETCH_ARRAY
      * fetches a row and returns an associative array (hash) keyed
      * on the column name
      */
      function fetch_array($result) { }

      /*
      * FETCH_OBJECT
      * fetches a row and returns an object whose members are the row's fields
      */
      function fetch_object($result) { }

      /*
      * INSERT_ID
      * takes an optional arg which is the table name
      * For MySQL, this is not required since this method
      * mimics mysql_insert_id() anyway, however, to get the same
      * information from other databases, we need a table identifier
      * PHP's postgresql driver requires the result index in order to get
      * the last insert id, so I made that an optional second argument.
      * This makes this class less generic (i.e., that's a change you'll have
      * to make in your code should you ever switch from mysql to postgres, for
      * example) but it couldn't be avoided. This method is a hack anyway.
      *
      */
      function insert_id($table = 0, $resulthandle = 0) { }

      /*
      * NUM_ROWS
      * return the number of rows in the specified result.
      * Only valid for SELECTS
      *
      */
      function num_rows($result) { }

      /*
      * AFFECTED_ROWS
      * return the affected number of rows in the specified result.
      * Only valid for INSERTS, UPDATES, and DELETES
      *
      */
      function affected_rows() { }

       /*
       * SET_ERROR_REPORTING
       * If > 0, db_query will call trigger_error itself.
       *
       */
      function set_error_reporting($new_val) {
            $this->error_reporting = intval($new_val);
      }
}

?>

line 69 which is referred to in the error is

$this = new $DBD_name($sql_host, $database, $sql_user, $sql_pass, $sql_port, $sql_dsn);
      }

Any help would be hugely appreciated as I am not familiar with php and got stranded with this.  Thanks in advance!!