imagettfbbox fails to return coordinates under distribution for win32 for PHP Version 4.0.6 using distribution binaries.  Unzipping PHP Version 4.0.4pl1 over 4.0.6 files and the example works again same config used for both.

here is sample script used to test

<?
   Header("Content-Type: image/png");
   $im = ImageCreateFrompng('C:\windows\backgrnd.png');
   $str = "Hello World";
   $font = "\\windows\\fonts\\CACVALIA.ttf";
//   print $font;
   $bbox = imagettfbbox(40,0,$font, $str);
// print $bbox;
   $black = ImageColorAllocate($im,128,128,128);
//   print "$bbox[0],$bbox[1],$bbox[2],$bbox[3],$bbox[4]";
   $start_x = ImageSX($im)/2 - (($bbox[0] + $bbox[2] + $bbox[4] + $bbox[6]) / 4);
   $start_y = ImageSY($im)/2 - (($bbox[1] + $bbox[3] + $bbox[5] + $bbox[7]) / 4); 
   $white = ImageColorAllocate($im,255,255,255);
   $red = ImageColorAllocate($im,255,0,0);
   ImageLine($im,0,0,200,200,$red);
   $gray = ImageColorAllocate($im,196,196,196);
   ImageTTFText($im, 40, 0, $start_x+3, $start_y-3, $black, $font, $str);
   ImageTTFText($im, 40, 0, $start_x,$start_y, $gray, $font, $str);
//   ImageColorTransparent($im, $black);
   Imagepng($im);
   ImageDestroy($im);
?>