Get the color value of a pixel in a texture or send data array

How can I, from a CG program in the fragment shader, get the color of the pixel (x,y) for a given texture?

My real question is actually how to pass an array of custom data to a shader, but I just read that unfortunately this is impossible with unity. If I'm wrong or there's another easier or more efficient workaround to do what I want that passing in a texture, please I'd like to know that as well.

Thank you very much!