Darklone, i think your analogy is slightly flawed here. an old western draw, as i understand it, is more of a simultaneous action than a turn based one, as the DnD combat system is. more appropriate rules for that might be the alternate jousting rules in that Dragon issue with the knights (don't remember the #). but, that's not main issue here ...
as Meepo said, you are always flatfooted till you first action in the round, barring uncanny dodge, regardless of how "unrealistic" it may seem. of course you might rule that initiative started when the monk bashed open the door (unless he did it on one try).
~NegZ