Footsteps script problem and question

Hi everyone, i'm having a little problem with a script.

I'm trying to add a running function but I'm affraid I can't. And why I cannot put anything under 1 in the inspector for the audiosteplength ? :|

Here he is :

 var walkSoundsWood : AudioClip[];
 var walkSoundsGrass : AudioClip[]; 
 var audioStepLength : int = 0.3;
 var groundType : int;
 var isPlayerWalking : boolean;
 
  
 function Update(){
    
 if(Input.GetButton("Horizontal") || Input.GetButton("Vertical")){
 
 isPlayerWalking = true;
 }
 else{
   
 isPlayerWalking = false;
 }
 }
  
 function Start(){
 while(true){
 if (isPlayerWalking == true && groundType == 1){
 
   
 AudioSource.PlayClipAtPoint(walkSoundsWood[Random.Range(0, walkSoundsWood.length)], transform.position);
 
 
 yield WaitForSeconds(audioStepLength);
 }
 else if ( isPlayerWalking == true && groundType == 2){
 AudioSource.PlayClipAtPoint(walkSoundsGrass[Random.Range(0, walkSoundsGrass.length)], transform.position);
 yield WaitForSeconds(audioStepLength);
 }
 else{
 yield;
 }
 }
 }
  
  
 function OnTriggerStay(type : Collider){
 if (type.tag == "Wood"){
 groundType = 1;
 print("Wood");
 }
 else if (type.tag == "Grass"){
 groundType = 2;
 print("Grass");
 }
 }

Thanks by advance :)

EDIT : Nobody ?