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The image/spacer.gif hardlinks are incorrect. If you enable spider friendly URLs the image directory tries to make itself relative to /reviewpost/showproduct.php/product/4 for example, meaning it's trying to find the image in /reviewpost/showproduct.php/product/4/images/spacer.gif, which is indeed wrong.
The image dir references in showproduct all need to have the global[idir] prefix added to them I think. Otherwise you get a briken image, or in FireFox the word "spacer" appears all over the screen