If you were previously a Zune user and log into Xbox Music with your Microsoft account, the service will display your local library as a virtual collection. Any video content previously purchased from Zune will likewise transfer over to Xbox Video. If you have any remaining Microsoft Points, you can convert them to your local currency by purchasing content or redeeming a code for Microsoft Points.
Although the Zune Marketplace is on its way out, Zune hardware will remain usable. Microsoft PR confirmed to Joystiq that owners of Zune hardware will still be able to enjoy playback of previously-purchased content from their personal collection on their devices.