Just been trying to familiarise myself with the  engine code 

{function OnCollisionEnter(hit : Collision)
{if(hit.nightwatchman.tag  ==  "Wall")  {
    Application.LoadLevel("level2"); 
 }
}function OnCollisionEnter(collision : Collision)
{if(collision.nightwatchman.tag == "Wall")
{
  print("collision occured");
}else
{
   print("no collision yet");
}
}} 

Don't know if this works yet but we'll see...

Aidan