I know that there is an official strategy guide for the game - most often referred to as the "Tome of Misinformation". I belive that there is a general monster description there, and I think Wyvern can tell you more about it.
So far as I recalled a former member of this board had also made a bestiary some years back, but I do not think it was posted to this board. I do not know if it is at all accesible at any site and how detailed it is...
Making a such seems a daunting task.
