Yes, this is possible with the solpart menu. If you look at the Skinning doc they show an example of creating multiple content panes leveraging the skin.xml file. In the doc you wil see CONTENT:1 CONTENT:2
It works the same way with the solpart menu. you will have the following in you skin.xml file.
<Token>[SOLPARTMENU]</Token>
<Token>[SOLPARTMENU:1]</Token>
You can then configure each menu in a different fashion one that is horizontal and only shows the root menu and a vertical one that starts at the first child. Really you can do many things with it.
I know this isn't very detailed, but I hope it will point you in the right direction.
Thanks,
John