What is meant by ventilation is to have small holes or screen ports in your enclosure so that air can circulate. Do not use fans etc near your tarantulas. The vibrations will upset them as will the air being blown at them.
actually i have not found tarantula or my other pet bugs to be that annoyed by vibrations. i am currently incubating a trapdoor eggsac about 5" from the computer i play loud music out of and they are doing great. they just molted to postembryos and hopefully in another week or three they will be full on baby spiderlings
as for fans... as long as you don't point the fan right at the cage, they aren't a big deal, either. during the summer i actually had a fan or two mounted to my bug rakcs a few years ago. didn't notice any negatives from it
i believe tarantulas are much more reactive to streamed CO2 rather than just moving air
I use active ventilation for all my citters including tarantulas. I pay attention not to bother them with vibrations, because the very first time I used it, I've attached the small fan right outside of the cage and the B.smithi went really mad.
On the other hand, if no vibrations exist, I could say that they rather enjoy the air flow, because when the ventilation is on, they are usually positioned in the screen area where the air comes from.