Problema con PHP y wiki thumbnails

[nachoz]

Hola comunidad,

Estoy tratando de usar el script del wiki http://www.forosdelweb.com/wiki/PHP:_%C2%BFC%C3%B3mo_Crear_Thumbnails_de_im%C3%A1g enes%3F

y me arroja los sgtes errores al tratar de llamarlo

Warning: imagesx(): supplied argument is not a valid Image resource in C:\xampp\htdocs\imag\imagen.php on line 7

Warning: imagesy(): supplied argument is not a valid Image resource in C:\xampp\htdocs\imag\imagen.php on line 8

Warning: imagecreate() [function.imagecreate]: Invalid image dimensions in C:\xampp\htdocs\imag\imagen.php on line 9

Warning: imagecopyresized(): supplied argument is not a valid Image resource in C:\xampp\htdocs\imag\imagen.php on line 11

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\imag\imagen.php:7) in C:\xampp\htdocs\imag\imagen.php on line 13

Warning: imagegif(): supplied argument is not a valid Image resource in C:\xampp\htdocs\imag\imagen.php on line 14

Uso xampp en windows xp, la libreria GD esta activada ...