Can anyone suggest a good DVD (or series) that will help me and my dressage trainer prepare my QH for the english AQHA classes?

I need to see how differently the horse needs to be ridden (rein length etc) in AQHA dressage and hunter under saddle classes.

My trainer is a classical dressage instructor, so I'm hoping that we can manage between us to figure it out from a good instructional DVD, and book.

Thanks