Many themes come with a few different layouts to choose from. You can choose the right one for each page while editing the page by going to the Page Options and choosing the template you wish to use from the "Page Template" drop down menu
http://get-simple.info/wiki/how_to:page_editing
When a new page is created, it automatically uses the one named "Default Template" so it is best to figure out which template is the single column one that you'd like to use, make a copy and rename that default template - just to save having to reassign each and every page (even on a small site that can get pretty tedious).
EDIT : Here's a demo site of one of Tmbow's themes that is a great example (Timbow's demos are also always chock full of How To information.)
http://timbowgs.bplaced.net/seascape/
he main page explains how to get rid of the sidebar component (info that applies to many themes);
The Templates link shows the alternate one column template for this particular theme.
http://get-simple.info/wiki/how_to:page_editing
When a new page is created, it automatically uses the one named "Default Template" so it is best to figure out which template is the single column one that you'd like to use, make a copy and rename that default template - just to save having to reassign each and every page (even on a small site that can get pretty tedious).
EDIT : Here's a demo site of one of Tmbow's themes that is a great example (Timbow's demos are also always chock full of How To information.)
http://timbowgs.bplaced.net/seascape/
he main page explains how to get rid of the sidebar component (info that applies to many themes);
The Templates link shows the alternate one column template for this particular theme.