I can't believe I actually have to do any work at all to create folders (!!!), but amazingly, folder support does not seem to come default in umbraco. I sure hope this is fixed in future versions, it IS rather basic.
Instead, having once again spent time searching (sigh), I found this article in the forum. It's LONG but at the very end is the solution on how to create folders:
The built-in umbraco way of redirecting one node to another is very simple.
In the "Folder" docType, create a new property. Give it these values:
Name: Redirect to
Alias: umbracoRedirect
Type: Content Picker
Save the docType. Open your en.aspx "folder" node and you'll see the new content picker. Select the /en/home.aspx page. Save the "folder" node.
When you visit the /en.aspx page from the website you'll automatically be redirected to the /en/home.aspx page.
If you don't want a "folder" to automatically redirect to another page, just leave the umbracoRedirect Content Picker empty.
(As usual provided by Doug, who has reached the coveted 'umbracoholic' level knowledge - I bow to his powers).
The side effect of this solution is that if I add a folder 'restricted', then this URL fails:
http://www.kadonk.com/restricted
Not sure how to solve that, but I'm going to ask !
This solution of course also messes with my menu's, as the 'folder' now get's listed in the menu structure. Sigh. But since my menu script ignores content with "umbracoNaviHide=true", I can simply add a generic property to the folder document type with that name, and set it to true. If only there was inheritance in the document types, I could add this property just one to my main template, but alas, there is not.
Note: The folders created are purely virtual, as far as I can tell.
Note: Another useful discussion on folders (although somewhat frustrating to read).