Xbox Live Arcade on Xbox 360 has proven to be a wildly successful enterprise, both for Microsoft and for the third party publishers and developers releasing Live Arcade games. It is home to both original titles such as Bizarre Creations' 2D shooter Geometry Wars and classic arcade games such as Capcom's Street Fighter II' Hyper Fighting.
When contacted for comment, Microsoft acknowledged the existence of Panorama but would not confirm or elaborate on any particular features. It is possible that the company plans to announce the project during its Microsoft Gamefest conference in Seattle next week. Shacknews will be covering the event.
Update: Microsoft's Andre "Ozymandias" Vrignaud has addressed this rumor on his blog, stating that Panorama is the codename being used internally by Microsoft for the first stages of translating Xbox Live to Windows. Though he did not address individual features, it seems likely that early versions of Live on Vista will be less ambitious than what is described here, though Shacknews' sources seemed confident that this functionality is indeed something being planned. Again, Microsoft is likely to reveal something relating to this project in just a few days at its Gamefest event.