A tool like Matlab for NLP?
I have just finished my Ph.D. and have used some NLP in it. My university didn't offer any NLP courses. So I ended up teaching myself NLP. I used this book.

Which serves as a great introduction to NLP using NLTK (Natural Language Tool Kit). It gives a good introduction into programming with Python. So handy if you've never programmed in Python before too.

I would highly suggest using nltk from nltk.org (sorry can't post more than two links)

The book I used is now out of date as NLTK is now on version 3.0, the book mentioned previously is for NLTK 2.x. But the Authors are working on a new version of the book for NLTK 3.X, you can view the unfinished book here.

I would highly suggest using NLTK and if you're new to natural language processing. I would highly suggest you try and get yourself a copy of the following book: 

Foundations of Statistical Natural Language Processing by Manning and Shutze

Even though it doesn't contain any code, it servers a great introduction to natural language processing.