hehee... you might want to checkout IanM's new ASM interface

ASM is bonza for anything Ai, especially some as complex as creatures - god just thinkin about making a DNA based engine to develop unique characters based on hundreds of preset variables, then using them as the genome base to then have then intelligently learn.
i'd start off with making a tamagochi or something then like simple creatures and such like rabbits or dogs, then moving onto more humanlike creature with learning abilities.
shouldn't take more than a year to learn what you need to reproduce similar work to Creatures 1
don't worry about graphics or anything like that right now, just try to focus on the actual possible intelligence routines.
i have a small bug that follows the mouse around the screen and runs away when you get too close to it ... i'll have to dig it out as it was in DB Standard ran pretty nicely.