All php exemples on using GD library returns no image but trash characters like
<?php
header ("Content-type: image/png");


$im = @imagecreate (50, 100)
    or die ("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate ($im, 255, 255, 255);
$text_color = imagecolorallocate ($im, 233, 14, 91);
imagestring ($im, 1, 5, 5,  "A Simple Text String", $text_color);
imagepng ($im);
?>
returns 
?PNG  IHDR2d
?&?PLTE????[?˝? 
there is error reported in my log.

I'm using Apache 1.3.26, PHP 4.3, GD 2 and windows 2000.
my php.ini is configured ok, the phpinfo() returns that GD is installed and jpeg, png and stuff are supported.

Could this be just a misconfiguration? Or something else?