Puck - you beat me to it in explaining that OTTB's aren't necessarily high strung! Usually I find that their misbehaviour is as a result of not understanding what you want and then becoming frustrated. Just try to be clear and consistent with them - the love people and they aim to please so just make it easy for them to do the right thing and they will try their heart out for you!
I started riding TB's (on the track and off the track) when I was 16, over 12 years ago. Once you have been doing it for a few years and ridden a couple hundred, you find they are surprisingly similar! But a better riding companion you couldn't ask for.
Here's a couple tips for both looking for them and beginning with them that I wrote on another thread ages ago, just added a few extra things in:
-When you are looking at an OTTB, soundness is a real issue, especially with respect to leg/tendon/ligament damage. Vet checks are great but if you can't have a vet look at the horse, take someone experienced with you to look for soundness issues, old injuries, freedom of movement and conformational advice.
-Once they have finished racing, turn them out in a good pasture and give them a few months 'let down' period. They are fed some pretty potent supplements so it is always a good idea to let everything work it's way out of their system before you begin working with them. The key is good quality hay and roughage and plenty of it. Also, being at the track can be a very high stress environment for a horse so a bit of time off is always a good thing.
-When you bring them back into work, treat them like a green broke horse, sure they are fine to ride but they need to be completely re-educated to establish three even, balanced gaits. If it takes a month, great that is really quick, if it takes six months, don't worry the extra time spent in the beginning will serve you well in the future.
-Don't rush their training, just because they pick things up quickly doesn't necessarily mean that the basics are firmly entrenched in their mind. Be prepared for a one sided horse with dodgy brakes! They have only learnt how to do one thing - go really fast in one direction and....eventually.....stop. Lots and lots of work on the basics to teach them all the shades of grey in between flat out and stop.
-Get their teeth checked. Although some trainers are very good about regular dentistry they are few and far between. Most OTTB's will be 4-8 years old when they finish racing and many have never seen a dentist in their whole life.
-Be prepared that a couple of visits from the chiropractor may be warranted. Any OTTB that I have bought for myself has needed chiropractic work and benefited immensely as a result.
-Introduce new diets slowly and be ready for them to possibly drop some weight when they come off the track as you adjust them to a new diet. A racehorse diet contains far more calories than what the average horse is fed, again good quality roughage is key. Have your feed analyzed if you can and measure it by weight rather than volume.
-Before you take them out to compete, take them to a show without entering them in any events and see how they handle the atmosphere. Most OTTB's think they are back at the track when they see all the horses, trailers and commotion so taking them out without the stress of competing is a good way to ease them into competition life.
Lastly, be prepared that every time you are working with them you are training them, make sure that it is a step in the right direction and not the wrong direction! It will take time for them to understand the things you are teaching them. I love nothing more than working with OTTB's, it is truly rewarding. However, I love spending inordinant amounts of time working on simple things like transitions, flexion and stretching. If you want to be able to jump on and go for a ride then OTTB's aren't a good option in the early days. Not saying that this is what you want, just giving you a heads up that there is a long road of training ahead before you can do simple things that some people take for granted!
All horses deserve, at least once in their lives, to be loved by a little girl.