Well, do you want a dual spec foots skirmisher/javalry build? Or do you just want to sit a horse all the time?
Here's my build (long time horse thrower)
* Strength: 17
* Agility: 18
* Hit points: 52
* Converted: 0
* Ironflesh: 0
* Power Strike: 5
* Shield: 3
* Athletics: 4
* Riding: 6
* Horse Archery: 3
* Power Throw: 5
* Weapon Master: 5
* Polearm: 115
* Throwing: 110
Now, on this one, I have a shield, but it's not necessary. I use it for style, and it's saved my butt from a lancer I didn't see sneaking up, since you can't down block with throwing weapons in throwing mode. If you don't want to use a shield, you can convert the 3 shield into another point of Str, and go PT 6. Have fun man, if you're in NA, look me up, I'm more than willing to help you practice.