I need to split a a flat PNG image to it constituent layers an save it as a layered PSD. IS there a way?

Only by selection and promotion.

hah? care to elaborate?

Open the PNG file.

use the "Magic Wand", Lasso tool, Marquee tool ect to select each colour/area/shape etc that you want to go on different layers, then use Shift+Ctrl+J will cut the selection into a layer or Ctrj+j will copy it to a layer.

Layer -> Layer via Cut/Copy on the menu.

i font think that there is a magic one click way to convert PNG to PSD file ......will not that i know of