You need plenty of CFM or you will be standing around waiting for the compressor tank to refill between lug nuts. Check with the mfr of your air wrench for requirements. Otherwise just about any air compressor will provide enough pressure to break loose a few individual bolts.
your impact will only take about 95 PSI max... so any compressor will work even a pancake... but your going to want a bigger tank if your going to be doing things like sandblasting, alot of air ratchet work or anything where your going to be on it alot.. Home depot always has some good deals on compressors.. if you can afford it go with an oiled unit.. the oil less units are annoyingly loud
damn good luck with that...I have a craftsman impact, that does 900lbs or torque reverse and 700 forward on max setting, and had my compressor at 95PSI and those damn driveshafts bolts were just laughing at me!!! pissed me off, granted I didnt have an impact extension, but I had an 1/2 extension with the 12point socket and nothing.....
Driveshaft bolts are definately a HUGE pain in the ass.
Get the back end as high in the air as you can. Then, used your longest and strongest 1/2" ratchet or breaker bar, with a cheater pipe or something on it. About 3-4' total will do.
if you get an air compressor get a 240v 5hp upright,spendy(about 480 from sears) but once you have one you will use it alot, not just for breaking bolts.
It is not so much the pressure,although I have been running no less than 120 psi in all my air tools and normally in the 150 psi range on some tools on a daily base's for 20 years on some tools with no ill effects(heavy equip mech. by trade), it is the volume of the air the compressor puts out at a given pressure.