Well art is a big word
I admit, I'm no artist, but that doesn't stop me from making a wallpaper every few months. I know my way around in PS and that's pretty much all you need to get your imagination into something other people can see. I used to toy a lot with 3D which you can see below. I also made some maps for Quake3 but lost most of that after a hd crash.
For wallpaper be sure to check deviantART to get the right resolution.
