First things first: make sure the brake cable and housing is the correct length, i.e. it doesn't apply any rotation to the caliper.

With those particular calipers: http://velobase.com/velobase.com/Vie...1-ad1bd9de6a06 , there's a special wrench that grabs the exposed hex-shaped portion of the center bolt to make for easier centering. Since I bet you don't have that wrench, try loosening the caliper, pulling the left shoe all the way over, then tightening the caliper again. Squeeze the brake lever a couple times and see where the caliper centers itself. Repeat until you're satisfied or insane, whichever comes first.

With very cheap calipers, we used to get them snug and then use a punch on the spring close to the center bolt. This is a rough method of rotating the center bolt, and it tends to bend the spring. However, sometimes it's the only method that works.