I want some faces to use a different texture file. I open the new image in the UV window, unwrap those few faces in the UV Window, but i can clearly see that even that i have opened another image file, the old image file is being used…
Holy crap! You didn’t get instant “service” to your question at three o’clock in the morning (EST)? I weep for the world.
You don’t assign image textures to faces in the UV/Image Editor window. That’s just where you do your unwrap. You’ll need to assign multiple materials to your object, each with a different texture image. Then you break out the different materials to work on different faces in the Links and Materials of the Mesh Edit Buttons.
There are other ways to go about it, but it depends on why you’re doing this and what the final effect is that you’re going for.