Forum posters at Eurogamer unearthed a job posting seeking a C++ programmer for the development of Go for Xbox Live Arcade. According to Eurogamer, the job posting stated that, "this role will involve writing a Xbox 360 title for Xbox Live Arcade. The game will be an adaptation of the classic board game Go, and will support a 3D view and networked Xbox Live play."
The job posting looks to be missing from the page, so we're going to have to take Eurogamer's word that it once existed. Because of that, and since the project may never come to fruition, we're going to treat this as a rumor until we hear something through some more official channels. That said, we're extremely amused by the thought of Xbox Live younguns trash-talking their way through this traditional Chinese board game.
Microsoft had a Go variant, Reversi, packaged with Windows XP, but it does not seem to be included with Windows Vista.