I wanted to see how easy it is to set up a new theme for Drupal, and it is indeed very easy. Mind you, all I did was to take an existing theme(bluemarine), copied it, changed a few things in the css to make the text green, and installed it. So, if I had any design skills at all I'll be at it for hours, but the basic concept here is quite simple.

Step 1 - find a base theme to work with.
I choose bluemarine

Step 2 - copy that theme's entire folder into a new folder with a new name.
I copied themes/bluemarine to sites/all/themes/greenmarine

Step 3 - change your copied theme.
In your theme's folder you will find css, php, and png files.

Step 4 - upload into you sites/all/themes directory
Up to this point I was changing things on my own harddrive.

Step 5 - activate your theme and make it the default
Go to Home » Administer » Site building » Themes
Enable your theme
Configure your theme
Make your theme the default

It's just that easy!