Multitasking is more geared towards spellcasters.
As I understood it, each of your non-primary hands is an offhand. If you have multiweapon fighting and multidexterity it is the same has having two weapon fighting and ambidexterity for a normal character.
That is to say you normally get X number of attacks with your primary hand +1 attack for your offhand. Multiweapon and Multidexterity work the same way. X attacks with your primary +1 attack for each of your off-hands.
So your four armed horned cat flying purple people eater would get 1 attack with his primary hand and 1 additional attack with each of his off hand's for 4 total attacks.
Should he ever qualify for improved multiweapon fighting (like improved two weapon fighting), he will get 2 additional attacks for each offhand.
Should he ever qualify for greater multiweapon fighting (like greater two weapon fighting), he will get 3 additional attacks for each off hand.
Should he every qualify for perfect multiweapon fighting (like perfect two weapon fighting), he will get a number of attack with each offhand equal to the number of attack he gets with his primary hand from base attack bonus and he will instantly be smited from above for his insanely inaccurate ECL of +1.
Clear as mud? Good.