Adobe photoshop is considered the professionals choice and certainly has many new tools in 7 that PSP doesnt. PSP is considered lightweight and a hobbyists tool, though I have seen some astounding work produced within it. Personally I prefer PSP feel and UI but I have to admit with v7 of PS that adobe has made the gap between the two applications a little wider. You will also find that although some plugins will work with PSP that there are a lot more which are PS only. If it was a question of buying one or the other I would recommend PSP to get started see how you do (and because its cheaper), unless of course you were serious about using it as a tool rather than a PT hobby. As however you have both I would take the plunge and get stuck into PS, the learning curves a tiny bit steeper but it'll save you trying to learn a whole new app down the line. Just my opinion :)