How Add NormalMap

I get the following shader from http://wiki.unity3d.com/index.php?title=AlphaVertexLitZ , it works nearly perfect as it said:

 Shader "Transparent/VertexLit with Z" {
     Properties {
         _Color ("Main Color", Color) = (1,1,1,1)
         _SpecColor ("Spec Color", Color) = (1,1,1,0)
         _Emission ("Emissive Color", Color) = (0,0,0,0)
         _Shininess ("Shininess", Range (0.1, 1)) = 0.7
         _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
     }
      
     SubShader {
         Tags {"RenderType"="Transparent" "Queue"="Transparent"}
         // Render into depth buffer only
         Pass {
             ColorMask 0
         }
         // Render normally
          Pass {
             ZWrite Off
             Blend SrcAlpha OneMinusSrcAlpha
             ColorMask RGB
              Material {
                 Diffuse [_Color]
                 Ambient [_Color]
                 Shininess [_Shininess]
                 Specular [_SpecColor]
                 Emission [_Emission]
             }
             Lighting On
             SetTexture [_MainTex] {
                 Combine texture * primary DOUBLE, texture * primary
             }
         }
     }
 }

I want to add NormalMap feature, like "_BumpMap ("Bumpmap", 2D) = "bump" {}"

but I have no idea about the shader language. Appreciate if anyone can guide me how to achieve that.