I'm trying to make a connection to an Interbase 5 database with the following code:

<?php
	$dbh = ibase_connect('localhost:c:\interbase5\tutorial\tutorial.gdb', 'tutor', 'tutor4ib');
	$stmt = 'SELECT * FROM Country';
	$sth = ibase_query($dbh, $stmt);
	//while ($row = ibase_fetch_object($sth)) {
	//	echo $row->email, "\n";
	//} 
	ibase_free_result($sth);
	ibase_close($dbh);
?>

NOTE: The lines as comments are for testing purposes.

My problem is I get a dialog box with the following error message:

Unable to load dynamic library 'c:\php\php_interbase.dll'.

I made sure the extensions path is correct and the php_interbase.dll line isn't commented in php.ini like this:

extension_dir = c:\php\extensions\

extension=php_interbase.dll

I have been looking for a way to fix this on the web but I haven't found anything. Does this only work with Interbase 6?