[support] square pictures (a la imagecache) without too much tinkering ?

Hi, I'd like to have the pictures generated by the image module be square. I tried the imagecache module, because from the description it seemed to fit my need, but the image derivatives it created are not accessible from the other modules. In fact, I wanted to replace the 'thumbnail' predefined size with a square extract. Is it doable with drupal 5 ? Thanks, Xav