As far as I'm aware you can't put other content into paintshed, you can only use what is there (correct me if I'm wrong), so if that is the case, then I dont think you can
Not quite true. You can make your own Paintshed templates as Whitepass has done but it isn't worth the effort. Far better to learn to reskin using a paint package such as PSP or the Gimp. There are several tutorials around.