Are you talking about .hack//SIGN? The book could be .hack//legend of the twilight. They're two different stories, taking place at two different times.
"lovers were of all people the most disagreeable."
Well, there's also the special DVDs that come with the four PS2 games that you can only get...from the PS2 games. That, or you could probably find 'em on Ebay!
I love .hack but I'm will admit it will get very confusing at times like Big O espicially if you missed a couple of episodes like I have. I think creating a book with a different storyline is just one big plot to confuse us.
The only reason there is diffrent plots in the anime, manga, and game is because after all the episodes,books, and games are completed, you will see that they are all entwined together, but in diffrent time periods (manga takes place 4 years after the final game).
Alot of games come from manga bu this one was the .hack project which used the playstation 2, manga, and anime to spread out the storyline, thus making sure people who are attracted to the plot will go and buy this shit.