Not entirely clear what you're asking, if it's cluster by topic matter, or pick out specific named/physical entities or maybe sentiment analysis. Two good firs

Not entirely clear what you're asking, if it's cluster by topic matter, or pick out specific named/physical entities or maybe sentiment analysis. Two good first steps to look into, depending on your needs, are Bayesian classifiers and SVD (reduction of high dimensionality, the application to text processing was patented as Latent Semantic Indexing/Analysis, LSI or LSA, by IBM, I don't knnow if that's lapsed).