DISCLAIMER: I stopped using Paint Shop Pro with X2. So I'm only answering as far as what I know from X2 and below. I started digiscrapping with PSP7. With that said, I am a former Paint Shop Pro user, but I do not believe that you can use Photoshop styles with PSP. If you can, it's new to me as that is one of the biggest reasons why I jumped ship and bought Photoshop! PSP is easy to learn, but you are very limited as far as what you can do with the program, styles being one of them.
Templates, they are like sketches. You should be able to open the .psd template in your PSP. The only thing you won't see are the shadows as they generally do not transfer over to PSP. Some .tiff templates you can open, however I've never been able to get the layers when opening .tiff files, so I always used the .psd. With opening the .psd you will see all the layers of the template and be able to clip your papers to the paper pieces and place your elements wherever. Templates are just guidelines. They aren't the Bible, meaning you don't have to place everything exactly where they creator of the template created. You can use it as a base and go from there, wherever your inspiration leads. But with PSP, you should try opening/using the .psd and know/remember you won't see the pretty shadows that were created using Photoshop.