According to my friend - in Anne Rice novels, vampires can drink other vampire blood.
Last time I checked an Anne Rice novel, if a Vampire drank "dead blood" (ie: any stale or old blood that wasn't fresh from an alive or currently dying victim) it would die. From memory that's how Claudia (played by the very young Kirsten Dunst) dies in the movie "Interview with a Vampire". Or it could have been one of the other vampires. I forget these details.
Supposedly vampires can feed off each other, but it is purely for erotic/masochistic value only. No life-sustaining value comes from it. They just do it for kicks.
According the the "Blade" universe, Vampires must feed on fresh blood because they can't regenerate haemoglobin (despite being able to regenerate tissue after injury, but lets not wreck a perfectly good fable), and thus die after too long without fresh blood from living creatures.
Make of that what you will. And please excuse the tragic geekiness of this post. No, I'm not some pathetic emo goth wannabe. I even have a tan! Honest!