How can I setup two difference camera in Unity .. For example one for doing perspective rendering and one for orthographics rendering such as making InGame Mesh Based Gui to reduce the drawcalls overhead with GUITexture when I have loads of GUI Representation in the actual game.
The short answer to the question of how to set up two different cameras, one with a perspective projection and one with an orthographic projection, is: set up two different cameras, one with a perspective projection and one with an orthographic projection.
I'm guessing that's not really what you're asking though :) Is it 'layers' that you're looking for, perhaps? That would typically be how you'd associate certain objects with one camera and other objects with another. Other things you might be interested in are the camera 'depth' field (through which you can specify that the UI renders over the game world), and 'clear' flags (which you can use to make sure the UI camera doesn't erase what's already onscreen when rendering).