1. If you believe in god, why would the existence of aliens prove that god doesn't exist?
Read Genesis. God created the heavens, the Earth, Man and assorted other critters and varmints. God creating aliens is never mentioned. And the Bible is infallible, so UFOs with an alien crew would put theologists in a bit of a bind. And in the part about Noah's Ark, it is never mentioned that Noah rounded up two aliens.
I am not religious so I don't know the rules, but could it be, perhaps, that the bible tells a story of creation but not necessarily the WHOLE story? There are already a startling number of details left out (I imagine whoever actually wrote Genesis did this to keep it from being disproved), I wouldn't be surprised if another world and its inhabitants were left out especially if it's all something we were meant to discover on our own.