parse xml and wordpress

i am trying to use an xml file of a wordpress site to visually display frequently used categories on the site.  i am imagining a topo map where x axis = categories in posts that receive the most comments, y axis = categories used most frequently in posts, and z axis = number.  i am just trying to show one moment in time for now, with the xml file i have downloaded from the wordpress site.  

has anyone ever used grasshopper to pull data from wordpress sites, specifically categories and/or tags?  

i think that if i could pull data from the list that records the number of times categories are used, as well as the most commented posts and the total of their associated categories, then that would be all the information i would need.  

any suggestions?