Hi S,
Without knowing more details about the problem you're having, I'm going to suggest that your download and install the *.
It simplifies the process of creating amazon affiliate links and you don't need to worry about uploading images to your server because the images are pulled directly from Amazon's servers.
Hope that helps,
~ Teli
* Although it says that it's in Beta and only for WP 2.1.x, I've used it on WP installation's up to 2.3.x without problems. However, your mileage may vary and I accept no responsibility if your server blows up.