You seem to be working in Obj-C... is that a requirement? What are you actually looking at doing? Is this for english only? Does it need unicode support? Is this simple text, or are we looking at html/programming/etc...
What I am trying to get across is that you have not asked a solid question, so there is no way anyone could really approach answering it. You also do not indicate that you have researched this topic at all, as there are a whole lot of word parsing algorithms out there for different problem spaces.
executive summary: figure out your question first, then research it, then post.