Is there a good book written in English on Divya Prabhandam?
First of all, for those who don't know, the Naalayira Divya Prabandham is Nathamuni's collection of the 4000 verses of the Alwars. In any case, I know of two English translations of the entire Naalayira Divya Prabhandham, both of them online:
http://4000divyaprabandam.blogspot.com, which gives English translations and explanations for all the Alwar pasurams.
http://dravidaveda.org, which is a Tamil language website, so if you don't know Tamil you may need to use Google Translate to navigate it. It's primarily devoted to giving a Tamil translation and commentary for each Alwar pasuram, but the webpage for each Alwar pasuram also contains an English translation.
But if you're interested in Nammalwar's Thiruvaimozhi, the core part of the Naalayira Divya Prabandham referred to as the Dravida Veda or South Indian Veda, I have more resources for you: