The menu is set in your skin.  If you look at the default skins that come with the installation, you will see examples of both horizontal and vertical menus.  If you don't want to use solpart menu at all, simply remove it from your skin.  You can then either replace it with the skin token of the menu you want to use (eg: Telerik's RAD Panel can be used and has a skin token) or you can use a navigation module and add it to your page like any other module (eg: Bi4ce's Navigator).  Either method works fine.  Using a skin token, of course automatically adds/maintains navigation for you based on your portal pages.  Module level navigation requires you to add the module to each page, but you gain granular control of what's in the menu itself.