Fluid Width?

I really like the theme, but my customer wants a wider page. I guess "elastic" would be a better description of what I want.

I modified wildnerss/style.css with this. My CSS knowledge is pretty poor though and is mostly made up of what I have taught myself through the internet, so this may not be the best way to do it.

.Sheet
{
	position:relative;
	z-index:0;
	margin:0 auto;
	min-width: 780px;
	max-width: 1260px;
	min-height: 23px;
}

I've seen a couple themes that add dropdowns to the theme page to choose between a couple different page widths or even fluid. I would love this ability, but haven't really researched how it is implemented. I believe the Sky theme has this.