Is there a big different between psp and ps?

I just read in the other forum (D300) about always post processing your photos. Well I only did that with my gymnastics photos but never with my macro shots so now I'm a bit in a panic as reading about it, it seems quite normal for people to post process their photos.

I have paintshop pro 7 and was wondering if that does the job as well as for instance photoshop or would I be better off buying the newest version of a photo editing program?

Then, how on earth do you know where to start and what to enhance? Is there a book that you recommend?

Thanks in advance.