Personally, I don't think buying a book is necessary. The key things are:
1. The exam blueprint - to guide you
2. The documentation - to read
3. The software - to play
The items in the exam are all set based on the objectives in the blueprint, validated against the documentation, and I found that some items could only be answered by having had hands-on experience of what was being asked.
Can you do the exam first? Yes. Have a look at this post on my blog though: http://vmwaretraining.blogspot.co.uk/2012/06/vcp-common-questions.html?m=0