Note: This post is about the beta and is out of date. See this post, SharePoint 2010 Fixed Width Master Pages Revisited, for an approach that works better with the release version.
Edit: Since I wrote this post I found this one which has a solution I like better: http://styledpoint.com/blog/fixed-width-centered-sharepoint-2010-site/. I also recommend you take a look at Randy Drisgill’s starter master pages which you can read about here: http://blog.drisgill.com/2009/11/starter-master-pages-for-sharepoint.html.
I spent the last couple of hours attempting to make a fixed width master page for a 2010 project we’re working on. Everything was great except for the fact that I couldn’t get the scroll bars for the page to display! So, I started over testing as I went and the scrollbars disappeared as soon as I removed a certain <div>.
<div id="s4-workspace" class="s4-nosetwidth" style=" margin-left: auto; margin-right: auto; width: 970px; background: url(/SiteAssets/PageBackground.png) no-repeat white;">
I had to make the div a little wider than what I wanted to avoid a horizontal scrollbar. I’ll figure that minor issue out later.
Author: Doug Ware