you don't save it as png in c4d, you save it as either tiff or targa and then import to ps and then go to alpha channels and select the very first layer via ctrl+click and then go back to layers and drag it to open/new canvas
There you have it dude - hm.. There was a tut if you wanted to save a transparent PNG hm..I think it was on P2L site
doing the whole targa thing is terribly unnecassary, just select quicktime png (obviously not in his case :/ ) and check the alpha channel box, once its rendered youll have the transparencies saved much faster than involving PS
