Freddy...I'll make this real easy for you.
"All dock backgrounds"...meaning "Tiles" & "Side Docks" (which are also called "zoomers" by some people) should be placed in your c:/Programs/Stardock/ObjectDock/backgrounds folder. And that means when you unzip a file and the folders appear...you place the entire folder in the above mentioned location...not just what's in the folder Since you only have the free version you cannot used tabbed docks.
As far as icons/pngs you might want to use for your docks. Lets say you have Winamp or Xion or MediaPlayer to play your music and you want to use certain icons/pngs to represent those programs. Create a folder called something like MusicIcons or Media...whatever you want to call it. Place any images you find that you may want to use now or in the future for those programs in that folder and then move it to c:/Programs/Stardock/ObjectDock. Do the same thing for any themes or program types in which you may want to change icons for.