Hi Thomas,
I used styleshout-brightsideoflife as a starting point for a custom skin for this site but have changed it quite a bit. Its a good deal wider than the original and I had to edit the images in Photoshop to make them wider which was trickier than it might sound, it took som trial and error to get it looking right.
And as you've noticed, I changed the menu structure to have 2 levels of horizontal menu and then a treeview vertical menu for pages deeper than 2 levels. andreasviklund-02 has the same menu structure so I borrowed some things from it. Look in the layout.master file for that skin and you will see the addtional menus and site map data sources and their settings to achieve this type of menu structure. It also requires organizing the hierarchy of pages to work well with this structure. ie you can only fit so many pages at the horizontal menu level. andreasviklund-02-alt takes it a step even further with 3 levels of horizontal menu and then a treeview vertical menu. Each of the menu's has to be configured correctly but you should see the important settings to achieve it if you study the mentioned skins layout.master file.
Most of the other skins have only 2 levels of menu, a top level horizontal menu and then a treeview for deeper levels.
Before you start attempting to customize a skin, be sure and rename it to a custom name so that if you later upgrade it won't be overwritten.
Hope it helps,
Joe