Are you guys fucking serious?..." Install bearing cups with a hammer"!!!!???!!?
Thats as stupid as using a hammer to install bearings in your wheels.
All you need to install your headset (the right way and the easy way) is:
-A peice of 3/4" threaded rod 12" long ( but any size from 5/8" to 1" will work great), 2 matching nuts and 2 large flat washers.... and 2 large adjustable wrenches to tighten it down.
Take a nut and thread it on the bottom of the threaded rod, then put one flat washer on the threaded rod, then your bottom bearing cup, now slide it up through the headtube, then put on your top bearing cup, then the second flat washer, then the second nut. Now tighten it all down and it will press the bearing cups right in, nicely...without damaging them