I'm going to clarify what I'm looking to do as best I can. I have a review site, and have a custom post type set up for reviews. My regular posts have three existing categories that feed right into a special section in my header. I want to apply an existing category to one of my reviews. I tried to add 'category' to make it show: array('category','post_tag'). The categories then added to my reviews, and I selected one of the categories, but when you click on that category there are no reviews or any posts filled under it.
If anyone has any solution ideas, I'm open to ideas, and I hope I clarified it well enough.