When you install your plug-ins it should automatically detect Photoshop, I just did a quick search and I assume the Eye Candy plugin I saw is the same as the one you're talking about... it looks to be compatible
You should be able to just drop it in the Photoshop plugins folder. It would be located in Programs/ Adobe/Plugins. My thought is that most of them are made for both. I have PSP 5 but rarely use it. I'll experiment with it and see what I find.