In this post, I will give you some useful references about these two types of clustering methods: categorical vs topical clustering.
Categorical Clustering: ROCK algorithm
http://rss.acs.unt.edu/Rdoc/library/cba/html/rockCluster.html
http://en.wikibooks.org/wiki/Data_Mining_Algorithms_In_R/Clustering/RockCluster
Topical Clustering:
Sahimi (1996), Applying the Multiple Cause Mixture Model to Text Categorization, In Machine Learning: Proceedings of the Thirteenth International Conference, Morgan Kaufmann