3 columns?

Hi there, I'm a big fan of itheme but I would like to see an option for having 3 columns so that it fills out the page better. (the main content in the middle with two sidebars on each side the same size they are now)

I'm not too sure how much work goes into themes so how hard would it be to implement this? Is it a case of just editing the css files?

I'm hoping this would take you 2 mins to do so if you can give me the code thats great but if not any advice would be appreciated.

Thanks.