If you want to try CS4 which is available free on the internet, just click here and select Photoshop CS4 extended. As this is a trial version I would encourage you to try this first before you spend big bugs and figure out how it works and see whether it could cater your needs. Though some of the filters are in software but some of it you need to buy to make it more advance editing. Here are some of my editing.
My first attempt of creating storm clouds- thunder & lightning effect and blending layers First attempt of changing background as a portrait