Hello,
The Sitemap webpart produces the unordered list in its HTML layout, so you can style it using CSS stylesheets as per your needs. However, you might want to amend the HTML so that there are the headings of the major sections of your page. This could be achieved via the RenderedHTML property of the sitemap control - you will use standard ASP.NET methods to parse it. Such approach is discussed here:
http://devnet.kentico.com/Forums.aspx?forumid=36&threadid=7311 (there is described the CSS List Menu, however the principle is the same).
On the other hand, you could try to use 4 repeaters for this purpose and display just appropriate section of the web within each of them. This has a big advantage, you don't need to mess with HTML parsing, since you can define appropriate layout directly in the transformation.
Hope this sheds some light and you'll be able to achieve your aim.
Best regards
Ondrej Vasil