How to set to fixed width

Here is how you can set the width and center your site.
Style Manager for your style, go to Stylevars, then doc_width
Units = px (in my case)
Size = 975 (in my case)

Next,
Style Manager for your style, go to Stylevars, then doc_margin

Units = px (in my case)
Use the ‘top’ value for all sides = no (in my case)
Top = 0 (in my case)
Right = auto (in my case)
Bottom = 0 (in my case)
Left = auto (in my case)
If using CMS then make sure to edit the default skin to use on the content.php page, main options.