To fully utilize the half-step gearing you will need to shift both the front and rear derailers at times to get the true half-step steps. Many folks used to have small shifting charts taped to their stems.

http://www.sheldonbrown.com/gear-theory.html

slide down the page to half-step gearing and half-step plus granny for Sheldon's discussion.

If it were me I'd just go with a 52/42/small, where small is whatever your rear derailer will handle for chain slack wrap.

edit to ask: are you going to run a 5-speed freewheel on back? If so then you might want to consider the half-step to give you decent options for gear ratios. If you were/are going to run a 7+speed then I'd forget the half-step games. Unless you don't mind sorta-big jumps between shifts.

pps: nice looking bike.