Adam (assuming for the moment that he was not a figurative character) was, amongst other things: Semitic, male, called Adam, living in Eden, heterosexual, and so forth. Eve was Semitic, female, called Eve, living in Eden, heterosexual, and so forth. You certainly can’t infer anything about God’s wishes (much less commandments) by arbitrarily chosing one of those characteristics.

There are other arguments people have made about homosexuality, based on the Bible. They just don’t hold up. See, for example, from a 30sec google search: this analysis. It seems pretty fair (though I have read only a portion), and I especially like that the conclusion is an appeal not to let this issue divide people.

Therefore, homosexual couples are not entitled to, say, a *Catholic* marriage, and a Catholic priest need not be required to marry them. Homosexual couples are entitled to the same priviledges that the state awards to, say, Catholic marriages, but that is a function of the public contract, not the religous rite. All that is required is that the public contract is available to people independent of race, religion, etc. It is already the case that a couple can be married by the justice of the peace, independent of any religion. The justice of the peace, acting as a state official, then would be obliged to marry anyone who satisfies the legal requirements.