Kylie Minogue's song is the official lead for Moroder's album (there are pictures of her on a music video set recently, it's probably for that) so I presume her song will come in a few weeks and Britney's will either serve as the second single and be released a little before his album or not be a single at all and just come out with his album.
Or it will serve as Britney's lead single...I think someone mentioned that being a possibility but I'm not sure.