Need help with Background

I'm having trouble making the background color 1, 2, and 3 transparent. I'm also having a problem where the background looks like it's repeating drastically to the side and a little bit to the bottom as well... it doesn't seem to do this on all of my monitors, but it's absolutely TERRIBLE on my laptop which has a 1280 x 800 resolution.

Here's a link to my forum if looking at it can help you out.
http://omgwtftestforum.heavenforum.org/index.htm

I'm new to CSS so it'd be appreciated if you could explain things a little broken down for me to help me understand them.

Thank you so much! <3

Well I figured out how to center and fix my background image but it still repeats on the bottom.

Still looking for help with this.