Well, if I understand your argument correctly you say:
1) If God has created the universe, who has created God?
2) If you say God 'existed' in eternity, that's no proof for in that case the universe itself could've sprung out of nowhere.
(I hope I get these points correct)
The infinite intelligent designer argument implies causality. Everything, so we humans believe, in the cosmos has a cause. Life was formed on earth, the earth was formed from cosmic debris and gasses, just as the starts which ultimately find their cause in the so-called Big Bang, perhaps the first cause of the Universe (another question would be: where did this BB come from?). Reasonable alternative would be: the Universe's just always been there, it has no beginning or end (but then, we have some evidence of an expanding universe).
About causality, like I stated before, we view the world in causalities. If x, then y. We rely upon those causalities. Even if we don't want to. But to this respect, and it is almost not understandable, that like time, space and matter causality is just one of the elements of our universe. So if we agree, in logic terms, that if God existed he must exist outside the Universe or else He would be subject to His own laws, the laws of nature. Therefor above argument, tho a lot can be said about it, is false: the being of God implies He is not subject to laws of causation. I hope you understand where I'm trying to get--it's hard to use language to descibe something that cannot be described ;)
Another thing, about point two. You say if you believe in an eternal, or rather timeless God why not believe in an eternal universe? The difference here is that God is a Person, i.e. sentient being (for all we understand) and not a system. It depends ofcourse, whether you believe the universe is a cold and desolate where massive powers spread their influence over gigantic distances of unfathomable emptyness--or, you are a pantheïst and believe the universe has a soul or at least there's some intelligence outthere. In Christianity, furthermore in most Western philosophies the universe is a dead place, a large space with things flying around and all sorts of crazy stuff--but the intelligence, the Creator is not part of His creation (at least, until He decided to become human himself). Phoey...