Crowbar. And gloves - be careful with those tacks.
It's yucky, yucky work. Any crud in the carpet will come flying at you, the tacks will sometimes escape from the strips and stay in the floor (they're a real pain to find on a dark wood floor). It also depends on what's under the carpet. I was a lot more careful on my hardwoods than on the rooms with the plywood subfloor...while I hate the tack holes in my hardwood floors, I have to thank whoever put that disgusting wall to wall down as it kept the previous occupants from doing a refinishing hackjob on all my floors.
I had to do that at a commercial building I own. If the floor is concrete, go ahead and use hammer and screwdriver. If its wood, your better off with a crowbar, because the screwdriver can cause serious damage to the wood when ya pounding on it with the hammer. Either way, its not fun work.