Fresnel Shader and AlphaDiffuse (BuiltIn) problem

Hi all,
I have two problems, if someone can help me please...

First I'm looking for a Fresnel shader to apply on my materials game objects. In this case really need a optimized shader for old and integrated videocards.

The other problem is about AlphaDiffuse shader(built-in on unity). On my scene i have some Directional light and a concave gameObject, but when I modify the alpha channel this game object reflects much light.

see the images about the transparency problem

1.- With AlphaDiffuse: Now i see this effect on [0.2 - 1.0] alpha.



2.- With AlphaDiffuse: If the alpha < 0.2 i see.


3.- With AlphaVertexLitZ from Unify Community all is perfect, but doesn't work on old computers with old graphic cards


Thanks!