you can do this, rather easy too, in fact i was going to do it on my bronco II, but ended up junking the truck before ot happened. I be honest, i wouldnt have a clue how much air a typical a/c compressor on a truck puts out. however i do know, that with a small airhorn, the compressor of my BII, (and we tried it with my friends old cherokee, he was doing the on board air aswell) was MORE then enough to power the horn. it wasnt a big horn, but for whats it worth.
obviously, you would want to put a storage tank, somewhere on the vehicle, this way you can limitedly use airtools (such as a impact wrench), however if you just want to use it only for inflating tires, i suppose you could just run a hose from the compressor, you would still need a pressure switch, or else once you turn the compressor on, the pressure in the hose would shoot up very fast, and probably damage the compressor, or hose. with whatever setup you wanna do, it wont be too hard. and if you dont need your a/c, i actually suggest it....i beleave ethier this site, or BII.org has a page on doing a a/c air compressor setup, just look around.