Here are some great tutorials explaining the basics behind making your own theme!

IGZ Classic CSS Script - What You Need To Know
http://vicious.voobly.com/forum/thread/116150
By: Abrasumente


Gradients
http://vicious.voobly.com/forum/thread/115627
By: Abrasumente


Creating The Splash and UserTipTool and IM
http://vicious.voobly.com/forum/thread/115398
By: Abrasumente


Basics Terms in CSS Script You Need To Know
http://vicious.voobly.com/forum/thread/115347
By: Abrasumente


Basic Guide On Editing IGZ Classic Theme - Graphics
http://vicious.voobly.com/forum/thread/115344
By: Abrasumente


Please feel free to make your own tutorials as well, or contact a staff member if you know of any other useful tutorials regarding themes.

Thanks!