set up a sampler:

...
texture entSkin3; //entSkin3 contains the shadowmap
sampler shadowMap= sampler_state
{
Texture = <entSkin3>; // Texture Base
MipFilter = Linear;
MinFilter = Linear;
MagFilter = Linear;
AddressU = Wrap;
AddressV = Wrap;
};
...

add this to the pixelshader before that line (FinalColor.a = 1.0f; // prevent transparency):

...
float4 shadow = tex2D(shadowMap,In.Tex1);
FinalColor = FinalColor*shadow; // maybe you will want to have it brighter ...*(shadow+0.2)
...

its untested but should do the job