A few rumors began surfacing earlier this month that the Xbox 360 might receive a hardware upgrade option in the future in the form of a Blu-ray drive. The rumors stated that Peter Moore, a VP for Microsoft, had mentioned it. However, those rumors have been vocally dispelled by Microsoft. Rather, the comment was taken out of context, and was a more generic term stating that the Xbox was flexible. It seems unlikely they would go out of their way to support Sony or the Blu-ray standard in any fashion, so it isn't surprising at all that the statements were made:

"We firmly stand behind the HD DVD format as the best choice for consumers. Current reports indicating that Microsoft has a back-up plan, which includes Blu-ray support are incorrect. We're fully committed to HD DVD and have absolutely no plans to support other optical formats," Mr. Rodman states.
Will they change their tune if the Blu-ray ends up being in-demand? It seems unlikely, but isn't out of the realm of possibility, especially if the PS3 ever picks up.