There are a lot of background books available in the market today, but only few are reliable, so, I think it's best to go for one that contains a comprehensive database of references for both English and Japanese language, including a comprehensive list of movies that you can watch from the library. It must have a lot of resources, which will enable you to easily search for any characters, and their background.
This resource will also help you to know about the background of all the famous actors in the popular animated series of DBZ, and it will give you a complete overview of the story arc. You'll be able to see how the story evolved, how the character changed, and how he/she developed over the years.
The second most important thing that you need to do if you want to learn about the history and background of the characters from DBZ is to browse through the full text of the novels. This way, you will get a comprehensive picture of what is happening around the characters and what is going to happen in the future. In addition, you will get a lot of information from the author, which may not be available elsewhere. It's good to read a lot of books about the series to understand the story better.
When you're done reading the book, try to study some of the dialogue of the characters from DBZ. Don't simply translate it into English, because some of the characters may appear differently in your native language. To find the most accurate translation, you have to look at the original Japanese, and compare it with the English translation. Try to search for Japanese books that were written during the 80s, when the popularity of this animated series was at its peak.
A good way to enjoy the show in the meantime is to read the popular animation series on your own. You will not only learn more about the characters from the books, but you will be able to watch and enjoy them.
You can use popular online sites that offer a wide range of entertainment, such as MySpace, Facebook and YouTube to watch episodes of the series. If you can afford it, buy the whole series, because they will keep on coming every week and you may get a great idea of what the author wrote.