Lee's recent skinning tutorials address the DNN Nav Menu. Take a look at:
The other skinning tutorials are appropriate, too. Just think in terms of a different menu. You should be able to fill in the blanks. If not, ask for help.
There is a good document about styling the Nav menu that you will find referenced here
in the DotNetNuke forum about skinning. There are other threads, too, that refer specifically to the Nav menu.
The Snapsis menu comes with a good manual.