Asteroid Capture

Ok, first I believe most asteroids are carbonaceous, so we may have to take what we can get. Which have modest water 3% to 22% water and modest iron content in the form of olivine and serpentinite, with alot of organics for the remainder. But this will also make our candidates less dense then the Ni/Fe bodies that you were looking at.

Also our goal is not to get a shuttle engine to the asteroid and directly rocket it into position. Its to position a probe over the asteroid and 'station' keep in the direction we want it to move. Energetically cheap for the 'adjustments' to orbit we can make, using the gravity of the probe and modest fuel use. Also we only want to take a near earth asteroids, which we have a few to pick from, and make them true near miss asteroids. The aerobraking of the atosphere will be used to decelerate most of the orbital velocity difference between the asteroids original orbit and the high earth orbit that we need to then adjust to bring it to ISS.
http://www.b612foundation.org/press/press.html
http://en.wikipedia.org/wiki/Gravity_tractor

These websites describe the feasibility of moving an asteroid on the cheap with this method. Aerobraking for capture will take some more work but nothing that we haven't done with probes and the space shuttle countless times. Yes it is at higher velocity, but you're only goal is to get them into Earth orbit with out letting them 'go'. You can also use the moon to slow down their velocity.

Brooks