This is really cool art work. I'm not very familiar with this sort of artwork. Do you use a specific program for these? Sorry if this appears to be a dumbass question but I had a fascination with computer graphics and CGI type images and would like to know more from someone who knows about it.
I use Adobe Photoshop for all of my art - I'm currently using Photoshop CS4, but you can do digital coloring and drawing well enough on any version of the program.
The main tool that enables me to do digital art, however, is my graphics tablet. It's a pressure sensitive pen + pad that hooks up to your computer and allows you to basically draw like you're using analog media.