Click on the link to DEZ 2008, it is the serpentines video.
Okay, this is for Appylover and anyone else interested. I know this is a very simple exercise, but it is very effective in gaining control over the horse's head position, softening their response to rein and leg cues, helping them with their balance, lightening them up in the body, and helping them learn to carry themselves well (and not lean on you). I have found when I warm up doing this for 10-15 minutes, everything about my ride is better. If I have a hard time with focus from him, I do some of these serpentines, and it really gets his attention on me as well as softening him up.
I do have to say that I have found the need to do work with half halts when I am interested in riding with more contact, but doing this exercise has even helped him become more accepting, and better understand the half halts. He used to gape a lot with any contact, but now, he know how to respond lightly to light rein contact so that he doesn't feel the need to gape.
In the video, I did no warm up before this, and for best results would spend about 5 minutes on the ground and then 10-15 minutes doing it in the saddle (or bareback in my case :) ), but of course this is a video. :)
I did show the video out of order because I have been doing this for so long now, that I go straight to trotting the serpentines, but when you teach it, you do it from the ground, then at a walk, then at a trot.
The concept behind it is to ask the head into a position by moving your hand so that they should follow with their head. Do not pull, but hold constant contact, and if they do not follow with their head, add drive from behind to drive their whole body into the position (that is why you see me waving the crop and smacking myself with it too). When teaching at first, it is best to start with just one side. It takes a while sometimes (my boy knows it, so that is probably not what will happen at first. When he gets his head into position, hold your hand steady, stop turning with him, and he will be stopped by running into your hand, then keep pressure and drive backward until he drops his head into the desired position when backing. Pat and give a rest to think and digest what was learned. Get one side down well, and then start the other side. You will have to start from scratch, as horses don't transfer ideas like this from one side of the body to another.
When you have it from the ground, use the same concept of ask with rein, enforce with drive from behind, and reward with release. In this case, when he gets hie head into the proper position, and his feet are following the direction of his head, release so reins droop, and let him go straight for a few strides before asking for the next turn.
Please let me know if I need to clarify anything. Appylover, I think that at least the ground portion would be useful for you with Vega right now, and Gem could benefit from it too...if he seems worked up and spooky, do it from the ground for a while until it is clear he is focused on you. This takes a bit of concentration and effort from the horse, so it does help them get into training mode for other lessons and exercises. :)
Give it a try. :)