The base of a creature's attack bonus is not a Base Attack Bonus.  It
is a simple attack bonus for the body and general experience (the
"creature-base attack bonus").  It does not contribute to multiple
attacks per round, does not increase the skill cap on weapon skills,
and does not apply fully when the creature is in another form.  For a
creature that changes shape (e.g. dragon), figure it gets 1/2 of its
creature-base carried over to other forms, adding to the creature-base
for the other form (but not exceeding its own native creature-base).

Creatures get multiple attacks because they have multiple weapons.  If
they have character levels in addition, giving them +6 base attack,
then their primary attack gets an additional attack at -5 just as
though they were a human Fighter weilding a sword (except that that
the creature also gets one attack with each of its other natural
weapons).

The creature-base attack bonus, while not giving extra attacks per
round, may give other benefits of base attack bonus.  (NEED TO REVIEW.)
It at least counts for grapple, disarm and sunder checks.

When a dragon learns to change shape, it gets one identity in each
creature type it can change into.  The dexterity is typical for that
creature type, as modified by the variation of the dragon's abilities
from the norm for its native type.  (E.g. a dex 11 dragon will be +1
dex in any form.)  Constitution does not change from the dragon body.
Strength and appearance (despite Charisma) will both start average for
the creature type, as modified by the variation of the dragon's
abilities, and will improve at +1 per dragon age category.  A starting
form *can* have better physical characteristics, but the advancement
is still based on an average member of the creature type (e.g. stat
base 10, as modified by the dragon's own stats).

Maybe: Each later age category, the dragon picks up one more identity
for each creature type, but the Strength and appearance advancement
lag those of the initial identity.

Maybe: Creature "base" attack bonuses count 1/2 toward the BAB
requirements for feats, assuming the creature got life experience
while growing up.

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Many unnatural creatures learn more slowly, if at all.  Constructs
generally are incapable of learning or level advancement.  Demonic and
other elemental sorts of creatures (including vampires) typically have
a -16 learning penalty (as per the Teaching rules) and an experience
penalty of at least 80%.  Lycanthropes and most liches have a -8
learning penalty (lower for natural-lycanthrope children) and a 50%
experience penalty.

When a powerful creature tries to pick up levels, advancement is very
difficult.  But a dragon that can Polymorph into a weaker form can set
aside many of its powers in order to focus on learning (much like a
dual-classed character in 1st Edition).  I'm tempted to model this by
having *either* the experience scaling for CR (the "party level" value
in DMG3 table 7-1 on p166) *or* the amount of experience required to
advance a level (the "character level" value you use in PHB3 table 3-2
on p22) be based on the creature's full ability (e.g. +10 effective
levels) while the other of the two numbers would be based only on the
creature's character level (starting at 1).