How do I enable PCF filtering on an ATI Video Card with Direct3D 9?

I am developing a Direct3D 9 application and currently using an ATI Radeon HD 4550 video card. This card is supposed to enable PCF filtering when the surface of a texture(created with the depth/stencil usage and format D16) is bound as the depth/stencil surface.

I have bound the surface of the depth/stencil texture but PCF does not occur...Here is shader code:

float4 SampleShadowMap(float2 uv)
{
    return tex2D(g_SamplerShadowMap, uv);
}

float4 PS(float2 ShadowMapUV : TEXCOORD0, float depth : TEXCOORD1) : COLOR0
{
    float4 results = SampleShadowMap(ShadowMapUV);

    // the 'depth' value comes from vertex shader where the triangle's 
    // position vector is transformed by the shadow casting light's 
    // view-projection transform.
    return dot(depth < results, float4(0.25, 0.25, 0.25, 0.25)); 
}

I have read about PCF on ATI cards from here and here.

How do I get the card to perform PCF?