You can mount the windows 7 partition in ubuntu, copy over the music, then unmount windows 7 partition.
Or you can keep windows 7 partition mounted on ubuntu (dangerous). Then you can access your windows file from ubuntu all the time. Just make sure you don't wakeup to the wrong OS after hibernate, or otherwise you face the danger of a corrupted partition.
Or if you don't mind redo the partition, you can create a shared data partition. Put all your data, music, ... on the shared partition. Both windows 7 and ubuntu can access it. Just to make sure wake up to the correct OS when you hibernate.