In the course of my discussion with Ed Feser, below, and also in the course of re-reading this old thread from What's Wrong With the World, it's occurred to me that the following points might be useful:
All Christians believe that God made the universe and sustains the universe. All Christians also believe that God sometimes does things that in some sense "go beyond" making and sustaining the universe. We usually call those miracles. Some have argued that, if a particular "going beyond" was "front-loaded" into the initial conditions of the Big Bang, it shouldn't be considered a miracle. I'm rather against front-loading talk, because I'm inclined to think that it would look like an intervention whenever it came up anyway. ("Hey, God front-loaded the change from water to wine at Cana into the Big Bang so that it happened at the very moment that Jesus intended it to!") But either way, Christians are committed to believing that there are things that God does by special intention that goes beyond, "God continually sustains everything at every moment" or "God made the whole world, somehow."
This is why all Christians that I know of have some notion of the natural order or of what are usually called secondary causes. There is some sense in which it is true to say that the weather in my town today is probably not the result of special divine intention but rather of the secondary causes according to which God has built the world but that the voice from the sky at Jesus' baptism was definitely the result of special divine intention.
When someone promoting an ID argument says that it is probable that such-and-such a particular phenomenon (say, the visual biochemical cascade in some animals) was the result of intelligent design, he need not be saying that the cosmological argument (or some other version of the teleological argument) doesn't work, that God isn't a necessary being, that it is not the case that everything in the universe depends on God for its existence, that God doesn't sustain the whole world, that God didn't create the whole universe, or anything of the kind. He can be prescinding from addressing all of those heavier metaphysical questions. What he is saying is that it is probable that this particular phenomenon (not everything in the universe indiscriminately) was the result of special agent intention. And special agent intention just isn't what we mean by any of those other things. It isn't included in God's sustaining the universe or God's being the Ultimate Cause or any of that. Suppose that a philosopher claims that, even if only one electron existed in the universe, it would have teleology and would necessarily require that God sustain that teleology. Whatever force that claim or an argument for that claim has, that argument isn't an argument for special agent intention. The old Gilbert and Sullivan song says, "If everybody's somebody, then no one's anybody." If we restrict ourselves to some sense in which everything is, of necessity, "the result of" God, then we just aren't talking about God's special intention, and ID arguments proceed from particular noticed facts and the explanation of special intention for those particular facts.
However one parses God's ways of working out His special intentions, Christians have to have a distinction between God's creating and sustaining everything and God's acts of special intention, because without it, we can't talk about miracles.
So when someone making an intelligent design argument says that it is probable that x was the result of intelligent design, he is saying that it is probable that x was the result of special agent intention. And whatever one believes about God as the Necessary First Cause and so forth, one is completely free to regard it as merely probable that some given phenomenon in the world is a result of God's special intention and special act to bring about that intention.
Hence, an ID argument does not involve postulating a God who is not the necessary ground of being or anything of the kind. As I said, the ID arguments just don't have to enter into those ultimate metaphysical questions at all. An ID argument involves postulating that we can examine probabilistically whether some given phenomenon is the result of special agent intention--which, if God is in fact the Agent in question, means special divine intention. What is being treated as merely probable is not God's relationship to Everything That Is but some agent's (or Agent's) special intention, and acting to bring about that special intention, with regard to this particular arrangement or event.
It will be observed that in making these last two points I am explicitly rejecting any hermetic seal or wall between the creation of, say, animals and Biblical miracles. That is correct. I do emphatically reject any absolute claim to the effect that "creation is different." Our conclusions about whether some animal or aspect of biological life is a result of special divine intention should be drawn on the basis of all available evidence, and in many cases (as discussed in the voice in the sky example in the previous post) that evidence will be similar in kind to the evidence that allows us to conclude special divine intention and action in the case of miracles within human history. The "creating parts of nature, such as animals, in the distant past has to be special" insistence is simply not, in my view, supportable. People often attempt to say that it must be different on the basis of various philosophical assumptions, but I simply do not find those arguments convincing. Evidence is evidence, and is all of a piece.
In any event, from a metaphysical point of view, I think it is enlightening to hold that in some sense special agent intention and action constitute the merely probable explanation in ID arguments. This should lay to rest any objection that ID is rejecting a God who necessarily is the Cause of all things.