To install a skin, go to Program Files/Vstep/ShipSim2008/(or wherever Ship Simulator is installed)Actors/Objects/Harbour Patrol
there should be 3 or 4 folders, 001 Rotterdam Authorities, 002 Crocs Rule, 003 Rainbow Flyer
Make a folder called whatever you want the name of the skin to be, or prefix it with 001 (and rename the other skin beginning with 001) to make it the default skin. Paste the downloaded skin into the folder.
You can choose which skin to use when you place the P6 into a scenario in Mission Editor.
I have about 15-20 reskins installed in Ship Simulator.
I haven't reskinned a P6, but I think you just edit one of the existing skins in Photoshop, but I'm not sure so don't take that as Gospel. I wonder if anyone can elaborate on making a skin for the P6?