The above reference to Solpart menu should not be used.  Solpart menu was the Dotnetnuke menu provider, but it has been retired and we are told to no longer use it.  It is still a part of DNN only to support legacy skins.  At some point, it may be removed altogether and any legacy skins would need to be converted to a different menu provider.

DNN Nav is the current production menu for Dotnetnuke and is being continuously developed.  It currently supports both horizontal and vertical menus, and in the future will support unordered list style menu's that are seo friendly (currently, the unordered list rendering has some bugs to be worked out).  Anyway, you can do what you want in Dotnetnuke without the purchase of third party menus or modules, unless you want seo friendly main menu, then you'd need a third party menu provider which are really very inexpensive. 

There is very little that you can't do with DNN.  Most skins probably have horizontal menus as a means to avoid crowding the content areas, but there are many skins with vertical menus as well.  And a skin can always have the menu converted to suit your particular needs.

JOHN GIESY
DotNetNuke Hosting Expert

DotNetNuke 7 Hosting $70 /year
DNN4Less.com Team DotNetNuke