By LIZ SIDOTI, Associated Press Writer WASHINGTON - A group of gay Republicans who supported President Bush (news - web sites) in 2000 will air a television ad opposing a Bush-backed Constitutional amendment that would prohibit gays from marrying. The 30-second spot by the Log Cabin Republicans shows Vice President Dick Cheney (news - web sites) at a debate four years ago saying, "People should be free to enter into any kind of relationship they want to enter into." The ad begins Thursday in several states. The vice president also says: "I don't think there should necessarily be a federal...