Using DSM-IV criteria, one would not actually make a distinction between anxiety disorders and PTSD. Anxiety Disorders is simply the broader category and PTSD is one of the disorders which fall under the category of anxiety disorders. If the client meets criteria for PTSD plus criteria for one of the other anxiety disorders, both disorders would need to be considered for the treatment. How this would actually end up effecting treatment would depend on which two anxiety disorders the person had and what their therapy goals were. Did you have two specific anxiety disorders in mind?