Here are the tutorials of which I'm aware:
http://www.ac3d.org/tutorials.html
http://www.ac3d.org/ac3d/tutorials/
http://supercoldmilk.com/ac3dtut/index.html
http://www.snickwerks.netfirms.com/Elric/AC3D_Wing.htm
Unfortunately, there aren't a wealth of tutorials for AC3D specifically, but once you've mastered the basics, tutorials for many other apps (3DS, LightWave, etc) can be applied to AC3D.