O Neil, just a friendly suggestion: Please only post replies if you've actually got something to show for it, pointlessness really only serves to fluster people. Which is, sort of, the exact opposite of actually helping people.
Just a friendly suggestion, as I said.
Anyhow, as to the actual question in hand...it's always possible to simulate the player being or looking different in an intro, since obviously there's no big sign floating above you with the words "PLAYER" written on it :toocool: BUT, if you're suggesting the player could move about inbetween (interactivity, I believe you called it), then it's impossible to all my knowledge. You're stuck with the one model throughout the whole mission :-\
Hmm. Alas. You can allow the player to make choices with the use of the action menue by for instance using the "switchCamera" command (look it up somewhere for instructions), but again, no moving around will be possible. Simple as that.
not 100% sure about multiplayer...I don't think you can spawn as another model there either though...alas...alas...
Good luck anyhow!
Wolfrug out.