Actually Photoshop is more for enhancing or embellishing pictures. For composing digital art, you're going to use other programs in conjunction with Photoshop, like Adobe Illustrator or Macromedia Freehand.

There are modeling programs like Bryce 3D (http://www.daz.com) that allow you to create lavish landscapes, objects, human forms, etc. with very little graphics art experience. I was actually surprised to see how cheap this program costs now - $80 for version 6.0; it used to be $200 just 3-4 years ago.

There are some great sites on the web - active discussion forums like the one we have here, plus sites that have self study and course work type programs (some for pay, some for free). These are good places to start.