So you could do something like this (presuming your animation is called run):
You might need to create a new script with this in, put it on your character and remove the animation stuff from your other scripts.
function Start()
{
animation["run"].enabled = true;
animation["run"].weight = 0;
}
var lastPosition : Vector3;
function Update()
{
var distance = (transform.position - lastPosition).magnitude / time.deltaTime;
lastPosition = transform.position;
animation["run"].weight = distance / 2; //Or some other number depending on how fast it moves
}