i recently purchased a 1991 mazda b2200 it was already dropped i got it for a good deal but was wanting to put an air suspension set up on it and was wondering which way to go about it  

there are alot of options on how to do it. the front is pretty standard for a torsion suspension truck, and the rear has endless possibilities. check out these sites, and also the tech section of this site.
http://www.suicidedoors.com
http://www.airbagit.com
you could also custom mount a independent rear from a mazda rx-7, that would be pretty cool.  

yeah the options are endless!!!
over the axle
Cantilever
4-link
6-link
the list goes on and on!!!
What are you looking to get out of the truck...ride quality...cheap...or dont care as long as it is low..hahaha  

ok so what is the diffrence between cantilever and a 6 link  

a 6 link uses basically a regular 4 link, with 2 bars in the rear, mounted to the axlehousing using dogbones. the bags are mounted in a leveraged position in the middle(ish) of the bar. a true cantilever uses a bar/bracket with a bag on one end and the axle housing on the other. in the middle of the bar there is a pivot point, which when the bag presses up the axle is pushed down raising the truck. you can adjust the length of one side or the other to change the amount of lift thats achieved or the characteristics of ride. i think thats as basic as i can word it.