I’ve seen this stunt pulled in almost every 3D game I’ve ever seen, and I’m just wondering how it can be done with Blender (can it?). You are walking across the landscape, you get to your car/horse. You get into/onto your car/horse. You ride it around for a while, stop on some other part of the landscape, and get out/off. And there you are, on that part of the landscape! How is this done with blender? Wait! … I just thought of something! No, really! It’s replace mesh, right? Say it’s replace mesh! Ahhh… never mind. Just say what it is, I don’t care whether or not it’s replace mesh.
I think Blengine has a solution for it, because he made a gta looking little game. The person in the game has the ability to get into a car which was driving around in the little village. I think he can tell you how to do that. 
do you have a link to that its just what i need too.
Url = http://www.zerooneentertainment.org/blengine/oldGames/ , I think it’s lixer adventure or something like that, I don’t know it because I didn’t test the file if it is that one. I’ve still got 56 kb modem so downloading would take some time for me. But soon I’ve got ADSL 
You could have a horse, a guy, then when you get on the horse play the animation and then destroy both the horse and the guy and add a horse with guy on it object. Then to get off remove the horse w/ guy and add the guy and then the horse.
pooba
or simple remove controls from the guy and give them to the horse, then when u get off give the controls back to the horse.
Have a Horse and a Guy. The Horse is Not a Dynamic Object. The Guy is.
When the guy gets on the horse, the horse now Copys the position of the Guy. Using Python you can imitate it being a child of the guy.
At the same time the Guys logic Changes to Horse Logic.
Python is preferable when doing things complex like this.
-Luke