The fourth column in mercenary towns.

Not just any version, but Maya 6.0, because it's the only one that offers some clever features for the map editor, allowing you to insert models into it.
You can find everything here: http://psatkha.narod.ru/tutorial_ru.html

Maya 6.0 is actually only needed in the final stage, when the finished model needs to be "re-converted" into a format that the game (Heroes 5) can understand – but you can create models in any editor you're familiar with (or have a license for :D) – for example, in 3DMax.