Hi Peter,
If I am right, I think it should be the same. If you don't need a sidebar on a project don't include it else include it if you need.
the way i use to implement this is like so:
HTML
sample three col content
<div class="content">
<!--
if you don't need a column remove it- it does not affect the presentation
-->
<div class="leftcol">
</div><!-- /leftcol -->
<div class="rightcol">
</div><!-- /rightcol -->
<div class="main">
</div><!-- /main -->
</div><!-- /content -->
sample twocol content
<div class="content">
<!--
if you don't need a column remove it- it does not affect the presentation
-->
<div class="leftcol">
</div><!-- /leftcol -->
<div class="main">
</div><!-- /main -->
</div><!-- /content -->
sample onecol content
<div class="content">
</div><!-- /content -->
CSS
.content { overflow: hidden; }
.leftcol, .rightcol { float:left; }
.leftcol { width:250px; _margin-right:-3px; }
.rightcol { width:300px; _margin-left:-3px; }
.main {}