It's true that you need BD2K3 to accurately see the graphics of Negundo World, which uses BD2K3's graphics.
It didn't just say that on Martijn's site; it also said that in the original place for downloading Negundo World.
"NEGUNDO WORLD 3" Release !
Moderators: Flumminator, Zomis
The H. World levelset can be downloaded from http://www.bd-fans.com/RnD.html -- search The H. World on that page.