The only reason that's it's difficult for me to use the Bible as a reference, despite it's historical importance, is because God's mood seems to be inconsistent. That, or the prophets who wrote it got it all wrong. God is filled with anger, hatred, spite, and wrath - old testament. He's filled with love, compassion, understanding, and tolerance - new testament.
In the NEW testament, he seems to be loving and understanding, but still carries his old-testament-disdain for anyone who hasn't gotten to their comfortable point of faith.
Getting more to the point, it seems the scriptures written on homosexual relations are ambiguous.
Romans 13:1-2 (NIV): "Everyone must submit himself to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. Consequently, he who rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves."
Seems that the only thing preventing gay marriage is the LEGAL SYSTEM.
There is nothing in the scripture that forbids two men or two women to be wed under God.