Cito la FAQ sul monaco e il combattimento con due armi:
Can a monk fight with two weapons? Can she combine
a two-weapon attack with a flurry of blows? What are her
penalties on attack rolls?
A monk can fight with two weapons just like any other
character, but she must accept the normal penalties on her
attack rolls to do so. She can use an unarmed strike as an offhand
weapon. She can even combine two-weapon fighting with
a flurry of blows to gain an extra attack with her off hand (but
remember that she can use only unarmed strikes or special
monk weapons as part of the flurry). The penalties for twoweapon
fighting stack with the penalties for flurry of blows.
For example, at 6th level, the monk Ember can normally
make one attack per round at a +4 bonus. When using flurry of
blows, she can make two attacks (using unarmed strikes or any
special monk weapons she holds), each at a +3 bonus. If she
wants to make an extra attack with her off hand, she has to
accept a –4 penalty on her primary hand attacks and a –8
penalty on her off-hand attacks (assuming she wields a light
weapon in her off hand).
If Ember has Two-Weapon Fighting, she has to accept only
a –2 penalty on all attacks to make an extra attack with her off
hand. Thus, when wielding a light weapon in her off hand
during a flurry of blows, she can make a total of three attacks,
each at a total bonus of +1. At least one of these attacks has to
be with her off-hand weapon.
A 20th-level monk with Greater Two-Weapon Fighting can
make eight attacks per round during a flurry of blows.
Assuming she wields a light weapon in her off hand, her three
off-hand weapon attacks are at +13/+8/+3, and she has five
attacks (at +13/+13/+13/+8/+3) with unarmed strikes or any
weapons she carries in her primary hand. If the same monk also
has Rapid Shot and throws at least one shuriken as part of her
flurry of blows (since Rapid Shot can be used only with ranged
attacks), she can throw one additional shuriken with her
primary hand, but all of her attacks (even melee attacks) suffer
a –2 penalty. Thus, her full attack array looks like this:
+11/+11/+11/+11/+6/+1 primary hand (two must be with
shuriken) and +11/+6/+1 off hand.