i suggest looking at the game carnivores... they did something similar, and one hell of a great job (still one of my alltime favourites :P)

http://www.youtube.com/watch?v=SBAjnCl1iDc&feature=related

regards,

Formerly known as dennis_fantasy
Portfolio - http://www.designorhea.com/
Project - http://randomchance.cherrygames.org/