Asha, there were no Emperor clones in Zahn's novels. TheSessler is correct in saying it was Dark Empire. THere's also a radio drama version I've been trying to hunt down.

As for Vector Prime, it wasn't bad. I'm up to Balance Point in the New Jedi Order, but I took a break from Star wars novels(considering I made it to Hero's trail when it was released, it's a pretty long break). Personally though, I think Stackpole's books added so much to the series that they're my favorite of the five I've read fully. The parts with Elegos Akala gave much depth to the Vong, and I'd love to recreate the Ithor duel in a fanfilm.