I forget about Harry's dreams because Voldemort seems like he has that concession. But you're right Potterdog! No reason Sirius couldn't communicate through dreams. I'm still holding out for the broken mirror because Harry didn't throw it away. He just dumped it back in his trunk.

KaraC: Not reincarnation. More like a guardian angel, maybe a protective aura, a dream of the future, a vision in a mirror--something more elusive.