How does one set up a tent on concrete (how do Occupiers of Wall Street do it)?

Sandbags work for me. Or concrete blocks and rope.

Tents without stakes

Many tents can be set up without stakes – I usually don’t even take mine if I’m trying for an ultralight load. The tent will just be a little wobblier than if you had it staked. Hexagonal tents are slightly more wobbly than rectangular, but it’s not a big deal either way, so long as the wind isn’t too bad.

All ours in our parking lots require drilling, you could probably use sandbags, we do for windy days.

If you have an old-fashioned tent that does require pegs and guy ropes, then consider the purchase of a couple (or more) 2×4 studs of the appropriate length which you can use as the “base” for the tent, and into which you can pound nails or screw eyebolts as “virtual” tent pegs.

One of the stores here had their parking lot set up for tents. They used PVC pipes to create voids they can slide stakes into without damaging the concrete. They have metal covers that fit over the voids when they are not in use so customer vehicles and the voids will not be damaged.

We use sand bags and water filled umbrella bases. There are also tent weights available from E-Z UP® and similar companies.

I have seen tents set up on temporary wooden platforms made from Plywood.

Tie the guy lines down to something heavy. Sandbags, bricks, cinderblocks, big rocks, the stoner next door. Whatever you’ve got kicking around that isn’t going to move and isn’t in use.

I suppose that the tents have built in bottoms, or floors. So all their shit crammed inside should keep them in place. Maybe they have weights inside.

Sadly the Wall Street Occupiers have only a sporadic presence since they were forced out of Zuccotti Park nearly a year ago. Those who protest on the sidewalk now are not allowed to pitch a tent.
However, when they were pitched the tents are largely the free-standing kind, with stored contents inside keeping them grounded. Some tarps were strung on lines between the trees.