There are 3 'versions' of the game: the standard one, the Collector's Edition and the Pre-Order edition. The latter 2 come with a bonus disc that is mostly fluff, but do contain an extra merchant each as compared to the standard game.
The Collector's Edition adds a merchant called Deidre who can be found at the Adventurer's Mart. She sells items from another fine game, Planescape: Torment.
The Pre-Order edition adds a new merchant, Joluv, to the Copper Coronet. He sells ites from Icewind Dale.
The bonus.zip file probably contains these 2 merchants.
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"Butt-kicking for goodness!" - Minsc
"Cities always teem with evil and decay. Let's give it a good shake and SEE WHAT FALLS OUT!!" - Minsc
