I think it's looking good so far. Are you looking to add a BG scene, or just some enhancing colors around him?
... And yeah, I use PS-CS4 myself, and have also heard that they are two completely different programs. But know that a lot of people mention using both programs in their work. Though I don't fool much with the filters and stuff in CS4 myself, you can always post any questions you have in reference to PS, and there are a lot of people here that can probably help ya. I will help with anything I can, but I would say any questions just relating to PS itself would get better responses posted in the PS section. ... Some may not see you question if just posted in your sketchbook. And you can also check out all the older post in the PS section. Sure there is already some information there you would find helpful. :)
Look forward to the update.
... My Gallery