Gamespot got a chance to have a hands-on demonstration of Spore Creatures for the DS. They jump right into a saved game and started playing with an unevolved creature, and over a short period of time, finally got a chance to customize it. Also, it looks as if the game does have a storyline which involves creature-on-creature combat. Here is a snippet of the article discussing the creature editor they messed around with.
The creature editor is fairly straightforward. As your creature levels up (there’ll be 30 levels in all), you’ll gain more body points, which can be spent on a variety of body parts. Each body part will have a different characteristic, governing your social, attack, or defensive capabilities. You can focus on a single characteristic, if you like, or attempt to make a balance of all three. Attack and defense capabilities will obviously help your creature become more fearsome in combat, while the social characteristic will apparently help you become more appealing when dealing with other nonhostile creatures.