http://www.paintwithpearl.com/
basically like most pearls, it is a dry flake that is mixed with a base clear. this is then sprayed over the base colour of your choice. just like exXU1 said
the difference in teh styles is explained, but in a basic form, it is a differing of the size of the metallic pieces to change the effect the paint gives. my pics above are the flake, so large pieces are easily identified, where as a shimmer pearl is small pieces so it comes out as a colour change rather than flakey