I use GIMP for now, but originally used Photoshop. If you're interested, you can check out the GFX Resource List and get started. Some great help from the community http://www.ps3trophies.org/forum/use...rces-list.html
Get a copy of Photoshop and spend as much time as you can making stuff with it. I've been using Photoshop Professionally for over 12 years. Read lots of online tutorials and enter Photoshop contests to practice.