As of right now, there isnt (and probably never will be) a plugin to export/import killing floor mesh files and animations in blender.
It one of the things that always bothered me about modding. Most plugins are for commercial programs and not many people can afford them.
Im only bringing up blender as a free solution for those who want to start modeling but cant/wont afford 3Ds max. you still need someone with access to 3Ds max to get the models in-game however (legit or otherwise).
Blender is being used more and more these days (there are already exporters/importers for Dragon Age geometry for Blender) and its also a great tool for independent developers to create models and keep costs low.
3Ds max is the better program (at least in some ways) as its price tag suggests, but blender is very, VERY powerful for a 100% free program.
as for 2.4x vs 2.5x, besides the *.3ds exporting problem, i