Dear Friend, dont skip anything - cos tax is the scoring paper.
Buy new book for may exam - cos amendments will be applicable for you.
Meanwhile, finish service tax and VAT, and study the other static subjects like accounts or infotech
Since you are confused about the subject, please dont hesitate to join classes. Your aim should be exemption in tax and not passing. Proper guidance is necessary to crack the paper, which is going to be made practical also.
So strongly suggesting you at least do combine study with the people going for classes - with the good students, not your bestest buddies!:p