Scifi Fantasy with Babylon centaurs and computers [s]

[Xeno_reader]

So there are these mages I think they were called. they can travel between dimensions. in this world they often do things with computers.a mage dies and is helping his friend find his replacement they wind up with a dumpy teenager with a halfbrother (OR maybe cousin) who drinks three pot of coffee every morning and is named Nick. she gets this virus and they have to go to Babylon to get wishes to heal her. There is a centaur who goes with them I forget how he plays in. in the end Nicks mom was the villain and Nick and his cousin halfsister whatever were actually among the heirs.

It was about seven years ago I read this. The fron cover shows a jumping centaur along with the dumpy girl in a turtle neck sweater (I think green) carrying a computer and Nick in his leather jacket. I really want to reread this book because I think it was interesting

[Andy]

Diana Wynne Jones "Deep Secret" http://www.sfsite.com/07a/sec60.htm

[Xeno_reader]

Now I feel like an idiot. Diana Wynne Jones is book marked in three different book databases. but I was certain it was someone else. Why did it have to make me feel like an idiot. one of my top ten authors.

Thank very much though.