Ok, I already described two ways to implement a traditional website style navigation with multiple levels:

1. Using Categories after fixing the problem that category pages were made for showing blog posts ONLY. Default they show a selection of your blogposts, but with the plug-in Category Post, it is possible to show both page and post content when your user presses a category link.
2. Using Pages after fixing the problem that pages were made for static content ONLY. By using the plug-in Inline Posts, you can add specific posts to your page.As both Pages and Categories have support for defining sub elements, my idea is that you can tweek your theme (the sidebar template), to show a tree-structured page_list or category_list in any way you like: ie. horizontally, collapsed and expandable. Then I found the WP Menubar plugin, which creates a whole new table in your database called ‘menubar’
3. This solution seems right. The plug-in creates a new interface to the Tools area in your dashboard. Here you can create a new Menu, and assign menuitems to it. Then you can assign content in form of categories and pages you allready created. To make it work you need to download and install the plugin, add a ‘menubar-templates’ folder to your wp-content/plugins directory, upload a menubar template to it (this styles the menubar), and finally you must remember to add a line of code somewhere in your theme, where you want the menu to go: fx the header.

To download WP Menubar, please visit the WordPress Plugin Directory.
To preview a Menubar template, you can visit the WP Menubar demo site.

menubar-templates (the one I use here is wpm-Suckerfish.zip)
documentation

this doesn’t seem to work…

There is a “Category Page” plug-in that gives your category content page features.

This plugin will let you setup connection between pages and categories, in order to display the page content like a “header” for your category archive (theme tweak required). By popular demand, version 2.5 also ships with a shortcode like [catlist] that allows to display a list of posts from a certain category inside a post or a page.

more: http://wordpress.org/extend/plugins/page2cat/

WordPress lægger op til at man bruger systemet fortrinsvis som blog og giver udover blogindlæg, mulighed for at oprette en række statiske sider: pages. ønsker man at basere et egentligt website på wordpress, finder man dog hurtigt ud af at man gerne vil have den klassiske blog feature til at optræde på de statiste sider også. Man kan løse problemet ved at lave en menu af Categories istedet for Pages. Men så har man ‘sider’ der KUN er blog posts. Vil man have det hele: Mulighed for at layoute en statisk side, med blog postings i bunden fx. er man nødt til at installere et plug-in som den gode Aral Balkan har lavet – gammel Flash gut:

Hent Aral Balkans plug-in der tillader dig at have posts på en statisk side: http://aralbalkan.com/wordpress

To start creating your own wordpress theme, all you need is two files: index.html for structure and style.css for style. Takes you through cutting up your XHTML into php files, to ease your workflow, and putting it all together again in the index.php file.

Convert xhtml/css to wordpress by Drew Strojny

If you want to use wordpress as a website before a blog you’ll want your visitors to see a static page instead of the defaul list of posts. This can be achieved by using the opriongs in Settings >Reading. Here I can point to any page I would like to load first.

More tricks for the task of converting your blog to a website: WordPress as a CMS – Content Management System

from chapter 1 in WORDPRESS THEME DESIGN

“If you’d like to build up your XHTML, CSS, and PHP understanding, you can use this site to walk you through everything from basic introductions to robust uses of top web languages and technologies. All the lessons are easy, comprehensive and free at http://w3schools.com. “