shaping a western horse

Question
I haven't been riding for long, but I own two horses of my own. I ride western, and I've been studying the different ways horses are trained to move, like how they collect, and the position their heads are supposed to be in. I know enough to see that my horses haven't really been taught much more than their basic gaits, and I don't know how to teach them any of it. What books or videos can I study to see exactly how a western horse should be shaped, and how to train them to move in the right manner? I do things like the Extreme Cowboy Race and trail rides, so I'm not too concerned about them collecting to the extremes or lowering their heads much. I just want to understand how to teach them to bring their hind legs under them, and things like that. Is there anybody that could look at pictures or videos of my horses and tell me what needs work, or something like that?

Answer
Much of this will depend on how in condition your horses are to begin with.

Will they yield their hind/forequarters on the ground, back on command, neck rein, and do they respond to leg cues?

If not, those need to be addressed first.

I have included several links here for you, some to videos that will give you something to visualize, as it is hard to tell you what to do, without knowing where your horses are at.

http://www.youtube.com/watch?v=GXo6NkTx9yo&feature=relmfu  I have watched her videos, and while she sounds like she is talking underwater, the things she is doing are done well, and explained well.  Pay particular attention to the ground poles, as these are wonderful tools for training a horse to use its back end.

http://www.youtube.com/watch?v=BfCl795Sv4Y&feature=related  This trainer, Cleve Wells, explains things well too.

http://www.youtube.com/watch?v=i7xMIfjUE1g  This is one of the premier trainers, and explains yielding well.

The best thing is to find someone in your area, that can watch your horse, and you could take some lessons from possibly, to help you.  They will be able to assess what level your horse is at, and work from there.