You do it like this: http://simplebits.com/notebook/2004/09/08/centering.html
Please understand that Fireworks is not a visual HTML development environment. It is a Web graphics program that can produce HTML and CSS for mockups/prototypes. The code Fireworks produces is not robust. If you are building a live site, you should use Dreamweaver or a text editor and do it right.
ok i see. so i know this is a little bit out of FW forum, but can u tell me what i need to do to add to the CSS file to center the page? i actually tried adding some additional code and couldn't get it to do it.
The short answer is... To make an external style sheet and link it, you put your CSS in a separate text file. Generally a CSS file has extension .css.
In the head of your HTML file, you add a line that references your external style sheet:
<link rel="stylesheet" type="text/css" href="yourcssfile.css" />
You want to replace "yourcssfile.css" with whatever you name your CSS file.
Making a Web page is not like making a print-design. You can't just do it visually and expect a program to produce a file that can be viewed. You need to know what you're doing with the code.
Go through this SitePoint tutorial: http://www.sitepoint.com/article/html-css-beginners-guide/
The tutorials at HTML Dog are nice, too: http://www.htmldog.com/