Posting in the Magento forums has been disabled pending the implementation of a new and improved forum solution which should better serve the community.
For new questions please post at magento.stackexchange.com, the community-run support site for the Magento community. We will be providing updates on the new forum solution soon. For questions or concerns please email email@example.com.
I don’t quite understand what you are trying to do. Do you want to get the category ID’s that a product is associated to, or load all products associated to a specific category by using the category ID?