Minimap camera transparency

Hello.

I followed this tutorial on how to make a minimap using a camera that's pointing to the terrain:

http://www.youtube.com/watch?v=ZuV9Xlt-l6g

What I'm trying to figure out right now though, is how to make my map a little transparent.

The tutorial gives me a shader to use on my material, otherwise i'd just use a transparent one and go with that... but now that I have this shader, how do I make it so the map is transparent?

Shader code:

 Shader "Custom/Mask"
 {
     Properties
     {
         _MainTex ("Main Texture", 2D) = "white" {}
         _Mask ("Mask Texture", 2D) = "white" {}
     }
     
     SubShader
     {
         Tags { "Queue"="Transparent" }
         Lighting On
         ZWrite Off
         Blend SrcAlpha OneMinusSrcAlpha
         
         Pass
         {
             SetTexture [_Mask] {combine texture}
             SetTexture [_MainTex] {combine texture, previous}
         }
     }
     
 }

Meanwhile I'm trying to figure out shaders... thanks.