Content vs Structure?

Okay, I have a problem that's been driving me nuts.  Let's say you have 
a page that you want to have multiple style sheets for.  The XHTML page 
separates content in a way that's pretty popular these days.  It has a 
block for the header, one for the nav bar, one for the side bar, and one 
for the main section of content.  But say one style wants to have the 
links displayed in the side bar, for example, instead of on their own?  
This seems to be a change in the style of the document, and yet CSS 
doesn't seem to have a way to facilitate it.  One could argue that it's 
a matter of neither content nor design, but structure, as it would be 
nesting the links block inside the side bar block.  How could this fit 
within the paradigm of separating style and content?

      "Puuh..."                    ~ *POOF* ~
                             Dris
                                  - Random Signature #7 -