If I understand you correctly, you need one readily created base model (not aiming for the complete avatar construction like in Spore right?) that's rigged and preferably animated, the head should be replaceable and possibly 'malleable' (modifying facial features). Add-ons also replaceable, e.g. clothes, hair, facial hair, scars & tattoos.
Okay. So first of all, there are already some really cool, rigged and animated models around that you could easily use. Here are two:
http://www.blendswap.com/3D-models/characters/simple-dude-1-3-5/
http://www.blendswap.com/3D-models/characters/character02-rigged/
Now, I don't know if those can be loaded in Blender 2.49. I don't think there's an OgreXML exporter available for Blender 2.5 yet.
We've also got a very nice site on our wiki with a bunch of resources set up for you:
http://www.jmonkeyengine.com/wiki/doku.php/resources
From those resources you shouldn't have any problem finding a rigged model to use as your base avatar. Since you're going for basic, this probably ain't exactly down your alley, but it might be cool to check it out anyway:
http://makehuman.blogspot.com/